The House of the Dead: Remake Achievement Guide & Road Map

The House of the Dead: Remake
The House of the Dead: Remake Achievement Guide

Overview:
- Estimated achievement difficulty: 3/10 with cheats; 6/10 and skill dependent without [Achievement Difficulty Rating]
- Offline: 41 [1000]
- Online: 0
- Approximate amount of time to 1000

: 4-6 hours with cheats; 8-10+ hours without, and skill dependent [Estimated Time to 100%]
- Minimum number of playthroughs needed: 3 full plus some chapter replay, but plan on more like 5-6; each playthrough takes around 20 minutes
- Missable achievements: None [arcade style gameplay]
- Does difficulty affect achievements: Must play on Arcade difficulty for Blood Bath (25G), but other than that, all achievements can be earned on Easy. Additionally, accessibility options in the Gameplay section can be used to make the game easier without impact to achievements. Most importantly, cheats can be used with no impact to any achievements. More information below
- Unobtainable/glitched achievements: None

Introduction:
Welcome to The House of the Dead Remake, a remastered console version of the classic on-rails arcade game. If you grew up playing in arcades in the '90s, you'll feel right at home here. While the graphics have been remastered to be a bit crisper, this game still has the exact same feel as a cheesy '90s arcade game, especially with the hilariously bad dialogue. Being an arcade game, the actual game from start to finish is relatively short, at under half an hour, but you'll need to do multiple playthroughs to get all of the various achievements. This could be a pretty challenging completion, but thanks to cheat codes it's far easier. See important section on cheat codes below. Let's get started!

Cheat Codes:
Be aware that this game features in-game cheats, and none of them impacts any achievements. They can make this completion worlds easier than it otherwise would be, since they include God Mode and Infinite Ammo, among others. The intention with these cheats is that their use would be unlocked by reaching set milestones in terms of number of achievements. For example, once you unlock 8 achievements, and then another cheat code at 16 achievements, 24 achievements, etc. While this was the intention, you can actually input all cheat codes and enable them right from the start of the game. No need to play without them and unlock achievements first. They are all inputted from the main menu. Just make sure your cursor won't land on New Campaign, since each cheat uses

, and the cheat won't enable if you start a new game in the middle of it. I scrolled down a couple lines on the main menu and then input them. You also need to input them relatively quickly, but nothing crazy. If done correctly, you'll get a popup in green text saying "cheat code activated." There is nowhere to see what codes are active, to my knowledge. To deactivate a cheat, input the code again and you'll get a popup with red text saying "cheat code deactivated."

Here is the known list of cheat codes:

Infinite Ammo (no reloading):
God Mode:
One Shot Kill:
Unlock All Weapons:
Infinite Continues:

Infinite Continues is pretty pointless if you have God Mode enabled, but the rest make the game a piece of cake. Note that inputting the code for Unlock All Weapons will instantly unlock both Try this! (10G) and Full Armory (35G) on the title screen.

Abbreviated Walkthrough:
The following abbreviated walkthrough assumes you're making use of the cheat codes above. If you aren't for whatever reason, it would be far more challenging to combine so many things into single runs. It's in your best interest to break things up if you don't want to use cheats. I should also mention that there is no need to go in order as I've shown it below, and you can feel free to group together whatever achievements you want in different combinations. This is just how I progressed through the completion, which I felt was a pretty efficient way of tackling all of the achievements.

Playthrough 1 - Save All Scientists, No Damage, No Reloading, ARCADE Difficulty, Modern Scoring, and True Ending:
For this playthrough, set the difficulty to ARCADE and set the scoring to Modern. Assuming you activated all of the cheats above (or at least God Mode, Infinite Ammo, and One-Hit Kill), this playthrough will largely be pretty easy. You can't get hurt and can't reload, so the associated achievements Invincible! (20G) and No ammo wasted (20G). Your main goal on this playthrough is to save every scientist. It may sound challenging but it is very easy, especially with those cheats. It's important to note, as mentioned in Saviour (50G), that you only need to save all scientists on the given route you take through the game, not all scientists across all routes. There is a handy trick to make it so your run isn't ruined if a scientist dies. If that happens, pause and quit to the main menu. From there, choose Continue and you'll be back at the start of the chapter you were on, allowing you to try again. While you do have to replay the chapter, it's better than having to replay the entire game. Plus, everything is always the same when you replay, so you'll learn exactly where scientists are going to be. With Infinite Ammo and One Shot Kill cheats, it's really easy to quickly take out enemies before they kill scientists. Saving all scientists will automatically access the armory in the final chapter, giving you Secret Room (15G) unavoidably as long as all scientists have been saved. Finish off this playthrough, and since you used Modern Scoring you'll have flown past 62,000 points and will unlock the true ending for True ending (25G), Blood Bath (25G) for beating the game on ARCADE difficulty, and a bunch of other achievements.

Playthrough 2 & 3 - Normal and Bad Endings, Classic Scoring, Kill All Scientists, Collect All Items, Co-Op Optional:
You need to do two more full playthroughs of the game to get the other two endings. Unfortunately, you can't just play through the final chapter. You'll need to use Classic scoring to stay under 62,000 points (it won't be a problem at all) to get the two other endings for Normal ending (20G) and Third ending (35G). They both are somewhat RNG dependent since they need you to beat the game with specific digits in your score. You'll get one ending on your second playthrough and then need to hope for your third playthrough to end with the other score. Refer to Third ending (35G) for more guidance on how to ensure that happens. The other thing I recommend for this playthrough is doing it in co-op for two associated achievements. With cheats on, you can just idle the second controller and do all work with your main controller like any playthrough.

The other things you'll want to knock out in these playthroughs are getting all items in a single run (see Collector (30G) for how to route that and make it happen), and then spend one chapter in either of these two runs killing all scientists you see to unlock Psychopath (10G)

Mop Up:
Hopefully you got the two endings under 62,000 points above, but if not, you'll unfortunately need to run through the entire game again until you get each. The good news is that, while doing so, your time isn't wasted: focus on all paths for Traveler (15G), since this requires replaying each chapter a number of times. Along the way to discovering all paths, you'll unavoidably get Catch'em All! (35G) for all enemies too, since you can't proceed without defeating all enemies. With that all done, all that's left is mopping up any miscellaneous achievements you're missing. They're all relatively simple to do (although some might take a bunch of tries), so refer to the guide for the quickest and easiest way to mop up each miscellaneous achievement, wrapping up this completion.

Conclusion:
Overall, this is a really solid remake. Most of the game just feels like a remaster of the arcade version, but there are a lot of things peppered throughout, such as unlockable cheats, galleries, weapons, etc., that add to the replayability. It's a short and simple game that likely won't take too long to finish, especially with cheats, which is probably for the best since there is no variation with the campaign each time you play it, and you can only play through the exact same campaign and enemies so many times before getting bored. Hopefully you enjoyed this nostalgic journey, and congrats on the completion!

[XBA would like to thank Necrophage33 for this Roadmap]

The House Of The Dead

100
Unlock all achievements of The House Of The Dead!
Simply unlock all other achievements to unlock this one. Nothing finicky or buggy about this achievement, thankfully!
Agent

25
Beat campaign at any difficulty.
Refer to Blood Bath (25G) for more information.
Blood Bath

25
Beat campaign at ARCADE difficulty.
For this achievement, when starting up a new campaign, make sure to toggle the difficulty to ARCADE, which is the hardest difficulty. Then, you need to complete the entire game from start to finish (you cannot just load in the final chapter and play it).

With the cheat codes listed in the roadmap, this becomes trivial. In particular, One Shot Kill eliminates all enemies instantly and allows you to take down bosses in seconds, while God Mode ensures you don't die and use up all your continues before beating the game.

If you elect not to use cheat codes for whatever reason, the good thing about this game is that it's exactly the same every time you play it, allowing you to just practice and get used to what enemies come from where, as well as improve your aim against bosses. Save as many scientists as you can since they give health packs often.
Chariot

35
Beat Chariot at the end of first chapter.
Story-related; cannot be missed.

Shoot him in the obvious weak spot on his chest over and over. You'll need to do it enough to interrupt him as he steps toward you or he'll hit you. After enough damage (75% or so), he'll shed his armor, making it even easier to shoot his weak spot. Continue unloading on it to defeat him.
Hangedman

35
Beat Hangedman at the end of second chapter.
Story-related; cannot be missed.

Basically the same as the previous boss except his weakspot is on the other side of his chest, and he's flying. He will gradually send bats at you, but they're really easy to take down. Worst case, shoot down all bats first, then unload on his chest. After a set amount of damage, he'll fly off screen, fly back, and knock you off the roof. This is scripted and you can't damage him during this. While you're hanging and he swoops back, this is when you can start damaging him again.
Hermit

35
Beat Hermit at the end of third chapter.
Story-related; cannot be missed.

This boss is even easier than the previous two because its big head right in front is its weak spot. Simply unload on it constantly. It'll shoot out web (?) balls, which can easily be shot down. Then, resume shooting its head to finish it off.
Magician

45
Beat Magician at the end of fourth chapter.
Story-related; cannot be missed.

This is the final boss of the game, and he can be quite the pain. He dashes across the screen, and his weak spots are the obvious red parts on him that don't have the sleek armor, such as upper thigh on one leg and shin/calf on the other leg. You'll need to focus fire on these two parts of his legs to interrupt his attacks. He'll still often shoot fireballs into the air, and you need to shoot them down before they fall on you. This is pretty easy to do. Even with cheats, it's a relatively slow fight compared to the others. Focus fire on his legs and take out those fireballs to beat this boss.
Normal ending

20
Finish the game with the final score below 62,000 and the last score digit not equal to zero
Refer to Third ending (35G) for more information.
True ending

25
Complete the game with a total score of over 62,000
I'm not sure if it's even possible to reach 62,000 points with the Classic scoring the game defaults to, but if you change the scoring to Modern at the start of a new campaign, you will breeze past 62,000 points with ease. I set my very first game to Modern scoring, and with little memory of the game, I far exceeded 100,000 points. Use Modern scoring to make this ending trivial to achieve.

Note that you need to play through the entire game from start to finish for this to unlock. You may see this ending without playing through the whole game, but it won't trigger the achievement.
Third ending

35
Finish the game with the final score below 62,000 and the last score digit equal to zero
For the Normal and Third endings that require you to score below 62,000 points, use Classic scoring. In all of my playthroughs with Classic scoring, I never even came close to 62,000 points, so you don't have to worry about scoring too much. My best run was around 46,000 points.

As for the last score digit being either a zero (for this achievement) or a five (for Normal ending (20G)), there is actually a really easy way to guarantee you beat the game with the score you want to get the proper ending. For that, it's important to realize that any enemy you kill will give you a score with a five on the end (for example, 85 for a regular kill or 205 for a headshot/heavy kill), and any boss you kill with give you a score with a zero on the end. This is all for Classic scoring only, of course. Therefore, enemies as the only way to vary your score. So, play like normal up until Chapter 4, the final chapter, killing enemies and getting whatever score. It doesn't matter at all.

In Chapter 4 is where you can control your score to get the ending you want. Here is what Chapter 4 consists of:
1. Two pairs of enemies
2. Refight of the first boss
3. Refight of the second boss
4. Five or six pairs of enemies
5. Fight against the final boss
Since the enemies that you fight are in pairs, their 5s in their scores will cancel out, meaning the digit at the end of your score won't change. Likewise, the bosses' scores give you a number with a zero, so they won't cause your score digit to change. The only thing that will cause your score digit to change is the number of bats you kill during the refight against the second boss. Each bat you kill gives you 15 points. This is how you can make your score end with whatever you want. If you want your score to end in zero and it already does, kill no bats (or an even number of bats). If you need to change your score (either to a five or to a zero), then kill one bat (or an odd number of bats). Purposely wait until there are no bats near the boss's weak spot so you can safely shoot it without killing the wrong number of bats. As long as you have a five or a zero in your score after the second boss fight, that's what your score will end with at the end of the chapter.

If you mess up the second boss fight, you can just pause and quit to the main menu, then Continue your campaign to start the fourth chapter over again and retry, avoiding the need for a whole new playthrough.

As a side note, you can NOT just play through the final chapter to get these achievements. You'll see the appropriate ending but the achievements won't unlock. You need to play through the whole game from start to finish.
Ender

25
Discover all three endings.
Refer to True ending (25G) and Third ending (35G) above for reaching all three endings.
Hero

20
Save a Scientist.
Refer to Saviour (50G) for more information.
Saviour

50
Save all Scientists through the campaign.
This achievement descriptions is very misleading. You don't have to save every scientist in the game. You need to save every scientist in a single playthrough, meaning whatever routes you take through the game, you just need to save every scientist you come across.

This is quite easy to do, especially with cheats. In particular, the One Shot Kill cheat is very helpful for quickly taking out enemies in a single shot to save scientists. If you mess up and a scientist dies (either from an enemy or you), you can pause and quit to the main menu, then Continue your game to be back at the start of that chapter. Take the same route you did before, but now that you know where the scientists are going to be, it'll be easy to save them. I did this on my first run and only had to quit out and continue twice. Most scientists are pretty obvious and easy to save.

It should go without saying, but obviously don't use the grenade launcher or you'll easily and accidentally wipe out the scientists, sometimes without noticing.
Murderer

10
Kill a Scientist
Refer to Psychopath (10G) for more information.
Psychopath

10
Kill all Scientists at any chapter.
As the description says, you need to kill all scientists in a single chapter of the game. They need to actually die from you shooting them, not from enemies killing them, so bear that in mind. Also, like with Saviour (50G), it doesn't have to be every scientist on every route, just every scientist you encounter on whatever route you take in the game.

This is easy enough to do, and you can even use the same trick as in Saviour (50G) to reload a chapter to try again, but that's not really necessary here since it's easily done in the first chapter of the game. Using the grenade launcher is a great way to practically guarantee you kill every scientist, since the explosion tends to wipe out anything on screen.
Traveler

15
Discover all paths available in the game.
As the description says, you'll need to discover every possible route in the game in each chapter, of which there is a pretty decent amount. There is unfortunately no way to track which routes you've discovered other than keeping track yourself. What you can track in-game is which chapters you've found all paths in. From the main menu, go to Statistics and then scroll down to Travelled Distance. With it highlighted, on the right side you'll see the distance in each chapter, but below that you'll see the percent completion of each chapter. This is how you can see which chapters you've completed all paths and which ones you still need paths. For the purposes of mopping up this achievement, you can do it entirely through chapter select on the easiest difficulty. There are varying reports on when a path counts towards the completion total, such as immediately after you take the path, a short while after you take it, or only after finishing the chapter. Personally, I completed each chapter to be safe, but this achievement unlocked for me right in the middle of a chapter when I chose the final path, so I'll leave it up to you how conservative you want to me.

As for all paths in the game, doomedtolive on Youtube has created video guides showing all paths in each chapter in the format of a choose your own adventure style series of videos. While the work is hugely appreciated, and it's a fun and novel concept, for me it quickly became tedious to have to restart from the first video every time, as well as not having full visibility on every path in the game and being able to (mentally) mark off which ones I'd done. To help, I have created flow charts of each chapter to show at a glance all available paths in each chapter. Those charts can be found below.

Chapter 1:

Chapter 2:

Chapter 3:

Chapter 4:
No choices in this chapter.

Below is doomedtolive's YouTube video series for all paths, if you prefer to use videos.

Note that, for Chapter 4, there are no choices in this chapter. The only thing that counts as a path in this chapter is the armory you access after saving all scientists, when you unlock Secret Room (15G).
Collector

30
Collect all items in a single campaign.
With cheats in use, this is probably the hardest achievement in the game. Like with scientists, you need to collect all items in a single run, meaning whatever items you come across, not all items in all paths. This can be a little challenging just because some items you barely have any time to collect them before you move on.

Before attempting this, I highly recommend unlocking the grenade launcher. Refer to Full Armory (35G) for doing so. Its splash damage will easily destroy breakable containers with items without you having to actually aim at them, and then again you can collect the item by just firing the grenade launcher in the same general direction. However, be aware with this strategy that sometimes killing all enemies on screen with the grenade launcher (which will happen instantly with how strong the grenade launcher is) will cause the game to move on potentially before you've gotten the item. You therefore need to be careful to ensure you prioritize breakable containers before killing all enemies (or do both at the same time).

It's definitely possible you could just wing this achievement with the grenade launcher and just fire it off constantly and get lucky to get all items in a playthrough. However, I've found that that strategy highly depends on the route you take. Some routes have items that are easier to spot and collect (such as being right by or behind enemies, or obvious on your path), whereas other routes have containers with items that are way off to the side of the screen and really tough to notice.

To eliminate the randomness from it, below is a video showing all items in a given route. Worst case, follow that route exactly and make sure you get the same items. If you miss one, you can use the same trick from the scientists: quit to the main menu and Continue your game to redo the current chapter rather than starting all over. Note that in the comments of this video, someone put together time stamps of all items in the video, which is also helpful.
Catch'em All!

35
Collect all creature entries.
This will come naturally while working on Traveler (15G) considering you can't move on until you kill all enemies on screen, in general. Therefore, while replaying the game and working to discover all paths, you'll naturally kill every enemy in the game. Just be aware that, in order to unlock this achievement, you need to actually enter the Gallery from the main menu. The achievement won't just unlock as soon as you kill the last enemy type.
Headhunter

25
Fire off 666 heads!
This is cumulative over your entire time with this game, any mode, win or lose. You will almost assuredly unlock this naturally well before finishing everything else. Personally, I actually unlocked this while using the grenade launcher to just plow through chapters, so you actually don't even need to worry about using a gun and aiming for the head necessarily. If you somehow find yourself still in need of this achievement though, just replay chapter 1 and use the starting gun to make it easiest to just aim for the head.
Sadist

20
Devastate opponent's body as much as possible!
If you're using cheats, I'm not sure that it's possible to get this achievement with One Hit Kill turned on. Even using the Assault Rifle, I wasn't able to shoot an enemy enough before the screen would transition and keep moving. However, with the grenade launcher this achievement will unlock with the first enemy you kill, most likely. The grenade launcher with a direct hit will definitely unlock it. Refer to Full Armory (35G) for unlocking the grenade launcher, or just input the cheat code in the roadmap to get it. Then, just shoot any enemy with it and this achievement will unlock.
Triple-Kill!

15
Kill 3 enemies in a row.
Refer to Penta-Kill! (25G) for more information.
Penta-Kill!

25
Kill 5 enemies in a row.
Note: This achievement requires you to turn on Modern scoring, which gives you bonuses for multi-kills.

The description is a little misleading. You need to kill 5 enemies in very quick succession. With Modern scoring on, you'll see the bonus on the side of the screen indicate a penta-kill if done fast enough.

The best place to do this is right at the start of the first chapter. When you get to the bridge at the begining, make sure to save the scientist being carried by the big zombie. Right after you save him, there will be five slug enemies on the bridge itself. Kill them quickly to unlock this. The easiest way to do this is with the grenade launcher, since a single shot will wipe them all out instantly. It's still possible with the gun if you're quick though.
Butcher

25
Kill 666 enemies.
This is cumulative across your entire time with this game, any mode, win or lose. This is essentially unmissable as you go for the completion, because you'll need to do three full playthroughs, and this will unlock most likely by the end of your second playthrough, but definitely by the end of your third.
Swifty

20
Shoot down enemies projectiles 50 times.
This is cumulative over your entire time with this game, any game mode, win or lose. Lots of different enemies will throw projectiles at you, and shoot them is what you need to do for this achievement. Actually, even using the grenade launcher works, as the explosion will deflect enemy projectiles too. Personally, I got this without even trying by the end of my second playthrough. Considering you'll be doing more than that, this is pretty tough to miss. If you somehow need to grind it out, just keep enemies alive that throw projectiles at you and keep shooting them down.
Not this time!

20
Finish single chapter without taking any damage.
Refer to Invincible! (20G) for more information.
Invincible!

20
Finish whole campaign without taking any damage.
This would easily be the hardest achievement in the game if not for the cheat codes. Use the God Mode cheat (as well as Infinite Ammo and One Shot Kill) to make this achievement trivial. I should note though that God Mode seems to be a little finicky. I have had instances where I still took damage from an enemy despite the cheat being activate (and working against other enemies). I suspect this has to do with killing scientists, which causes you to lose health. I'm not entirely sure if killing a scientist voids this achievement, but I would recommend saving them (or just letting them die) rather than killing them with, say, the grenade launcher. It's therefore pretty simple to pair this achievement with the same run of the game where you save all scientists. That's also the shortest path possible, since saving scientists typically leads to a shorter run through the game.

If you decide not to use cheats for whatever reason, this will be decently challenging, especially against the final boss. The good thing is that you can break this up by chapter, similar to other full-game achievements like saving all scientists. By that I mean if you do take damage, quit out to the main menu and then choose to Continue. You'll have to start the chapter over, but it's better than starting the whole game over, and it lets you take it one chapter at a time instead of having to do the whole game start to finish without getting hit. What's also nice is that there is nothing randomized about this game whatsoever, so retries in this manner mean you can eventually lean where all enemies are and who to shoot first to ensure you don't get hit. Without cheats, it's really just a matter of practice makes perfect.
Agent G

10
Finish full campaign with your friend!
As the description says, you need to play through the game from start to finish in co-op. When starting up a new campaign, make sure you enable cooperative mode (or competitive, if you want), and then have two controllers set up (there is no online play). There isn't much different in co-op other than some extra enemies here and there. If you're using cheats, it's really easy to just leave the second controller idle and play through like normal with your main controller. Even without cheats, on Easy it's still completely practical to play through solo considering you have so much health and 10 continues.
Partner

10
Finish any chapter with help of Player 2.
Refer to Agent G (10G) for more information.
Reinforcements!

10
Let Player 2 join the game while in a middle of a campaign.
To unlock this achievement, you need to make sure your second controller is turned off (and/or unplugged) so your console and the game don't see it. Then, start up a new campaign and enable either cooperative or competitive mode. As long as your second controller isn't visible to the game or console, it should let the game start without needing to ready up your second controller. Then, once the game starts, simply turn on your second controller and join in to unlock this achievement.

As a side note, I have seen other solutions required ridiculous things such as powering down your console, hard resetting, juggling controllers back and forth, etc. None of this is required. I play with a wired controller. I simply did nothing with my wireless controller, keeping it off. I went to New Campaign, enabled cooperative mode, and then after the opening cutscene I turned on my wireless second controller, joined, and achievement unlocked.
Who let the dogs out?

15
Knock back the Kenfis
This is an oddly specific achievement. Kenfis are the little winged dog-like enemies. Right near the start of the game, two of these enemies will jump over a concrete wall. For this achievement, you need to knock either one of them back over the wall.

I'm sure this is possible with a gun and good timing/aim, but you can also use the grenade launcher and its explosion. You still need to time it right and shoot in a spot that'll send them in the right direction, but since this is right at the start of a new game it's pretty easy to continually retry. Below is a clip of when I successfully unlocked this achievement.
Ringo

15
Knock up an enemy as high as possible.
As the description says, you need to shoot an enemy over and over to continually knock their body into the air high enough for this achievement to unlock.

I'm not sure if this is possible with any gun other than the Assault Rifle. Refer to Full Armory (35G) for unlocking it.

The Assault Rifle has huge knockback already, and you can hold down either or to fire nonstop, making it way easier to do this. I should also mention that there are reports that this isn't possible with One Shot Kill cheat enabled, but I got it with it on.

Here is a clip of me getting this on a random enemy. I was trying for this on any enemy and was surprised the achievement unlocked here because I didn't think I knocked them up particularly high. I got it on the enemy above me on the ledge.

https://www.xbox.com/play/media/isacQ5qUKL

Here is a video showing a great place to get this achievement, right near the start of Chapter 2. If you're looking for a reliable place, this is the best I've found.
No ammo wasted

20
Finish level without reloading with bullets in the chamber.
With cheats, this is trivial and will happen automatically. Enabling the Infinite Ammo cheat means you'll unlock this without trying. Even without cheats, if you go into Options, there is a setting you can enable to auto reload your gun when your ammo is out. You can not only enable that, but you can specify how long it takes to reload. You can lower it to 0.0 seconds, meaning reloading is instantly. This eliminates the need to ever do a manual reload in the first place, again guaranteeing you unlock this achievement, if you don't want to use cheats.
Unwinged

25
Shoot all Hangedman's Devilions.
This achievement requires you to kill all of the bat enemies around the second chapter's boss.

If you're playing with cheats on, especially One Shot Kill, be careful to avoid shooting the boss because all bats will disappear if you end his first phase.

Simply pick anything other than the grenade launcher to be safe, and just watch the bats. One or two will fly at you every few seconds. Just keep shooting them. You can shoot the ones flying around the boss too, but be careful you don't miss one flying at you. They will all eventually fly at you, so just take your time and shoot them all, and you'll unlock this achievement.

Secret Room

15
???
This achievement is unlocked by saving all scientists on a single playthrough. Refer to Saviour (50G) for doing so. If you've saved all scientists in the first three chapters (there are none in the fourth chapter), when you get to the fourth chapter you'll eventually head down a hallway, and you'll automatically enter the armory if all scientists have been saved, unlocking this achievement along the way.
Full Armory

35
???
This achievement requires you to unlock all four weapons in the game. There are two ways to do this.

The easiest and fastest way is to input the Unlock All Weapons cheat in the roadmap. This instantly unlocks all weapons as well as this achievement right on the title screen.

The longer but "legit" way to unlock all weapons is to first open up the armory. See Secret Room (15G) for that, but basically you need to save all scientists in a single run through the first three chapters, and then you'll automatically enter the armory during the fourth chapter. Once you've done this, the weapons are now available to collect in the game. Here is where each is located. If you refer to my flow charts in Traveler (15G), it'll make it easier to see where these weapons are.
1. Crossbow - Chapter 1 - Let the scientist be thrown from the bridge near the beginning, then save the scientist in the sewers. You'll then climb a tall ladder. At the top, the crate is on the left side of the screen
2. Pitter - Chapter 2 - Shoot the trap door in the beginning to go down into the kitchen. An enemy will break through the wall on your right, in the kitchen. The crate is behind him
3. Grenade Launcher - Chapter 3 - Near the beginning, in the room with the security keycard, in a crate against the back wall
4. Assault Rifle - Chapter 4 - Right at the start you'll fight two enemies, and then a second set of two enemies in front of an open room, and there's a crate on the right side to shoot open with this weapon
Try this!

10
???
Refer to Full Armory (35G) for more information.
Grenadier

20
???
You'll first need to unlock the grenade launcher for this achievement. Refer to Full Armory (35G) or just use the cheat code in the roadmap to unlock all weapons.

Once you have the grenade launcher, you need to kill 5 enemies at once to unlock this achievement. Pair this with Penta-Kill! (25G) to get both at the same time. Refer to that achievement for the perfect place to get it.
Dance Macabre

10
???
You'll first need to unlock the Pitter weapon for this achievement. Refer to Full Armory (35G) or just use the cheat code in the roadmap to unlock all weapons.

Once you have the Pitter, this achievement requires you to headshot an enemy with it such that their head gets stuck to the wall. Any indoor enemies will do, just aim for their heads and you'll quickly unlock this.
Really?

10
???
This achievement requires you to use up all 10 continues and then die and have game over. You cannot just die and let time run out and have game over that way. You need to use up all 10 continues first.

It's virtually impossible you'll do this naturally, just because 10 continues is such a massive amount of retries. If, like me, you still need this achievement when you're done with everything else, turn off God Mode (reenter the cheat at the main menu to deactivate it), then start up a new game with it set to ARCADE difficulty (so you have less health and take more damage). Now just idle on the first enemy of the game and let them kill you over and over. Make sure to continue each time you run out of health.

After your 10 continues are used up and you die again, you'll get a cutscene of your character falling over and dying. This triggers the achievement to unlock.

Note: This is obviously not possible with the Infinite Continues cheat on, so make sure you deactivate that at the main menu before attempting this.
Glass cleaner

20
???
This achievement takes place in Chapter 2.

Towards the end, you'll go into a facility with big test tubes of creatures inside. You'll eventually come to an open room with enemies across from you (pretty far away) and colored glass panes next to them. You'll then go around the side of the room and come to those glass panes again, having to kill enemies on both sides of them. This achievement requires you to get through this room without destroying any of those colorful glass panes.

It's easiest to just watch the clip below to see what area I mean. Below is a clip of me successfully doing this. Simply avoid the grenade launcher and stick to any other weapon. Shoot each zombie just enough to kill it, and keep your shots as far from the glass as possible, to be safe. It's easy enough to do when you actually try for it.

https://www.xbox.com/play/media/MbEAtCLCce
Deratization

30
???
This achievement requires you to kill five rats. There are only five, and they are in very specific spots. There is a group of three in the first chapter, another single one toward the end of the first chapter, and then one right in the beginning of the second chapter, in the kitchen.

This would be virtually impossible to explain in text, so refer to the following video to see where all the rats are. I recommend just spamming the grenade launcher in their direction to guarantee you kill them, since they're really hard to see.