Rock and Coil Hit Back Achievement in Halo: The Master Chief Collection

This Multiplayer medal is represented by a black skull inside a yellow triangle and is only available in Halo 2: Anniversary. It is awarded to players upon killing an opponent with any dynamic element in the level. This includes - and is unfortunately limited to - the stalactites in Lockdown, as well as the fusion coil barrels in both Lockdown and Stonetown. As a final reminder, this achievement will take quite a while to earn as there is no definitive way to boost Environmentalist medals.

Since there are only two maps that allow players to receive these medals, you're best bet when playing Multiplayer is to stick to the following playlists: Halo Championship Series or Team SWAT. Lockdown will appear in both playlists (more commonly in HCS). Stonetown on the other hand will appear in Team Halo 2: Anniversary, Halo 2: anniversary Rumble, Team Slayer, and Big Team Battle. Despite this, Team Slayer and Big Team Battle are not recommended because Stonetown has a very low probability of appearing as one of the maps. It has a greater chance of appearing in Team Halo 2: Anniversary and Halo 2: Anniversary Rumble, however Stonetown doesn't have as many fusion coils as Lockdown.

With this in mind, stick to the Halo Championship Series playlist or the Team SWAT playlist. Environmentalist kills are not always guaranteed every match, however if you're keen on shooting down the stalactites every so often during a match - or happen to shoot a fusion coil while an opponent is camping near the "Sniper Tower" or above the "BR Tower" - you may be lucky enough to earn yourself an Environmentalist medal if these objects kill the enemy player.

All in all, this achievement goes only as far as a player's luck and skill in luring enemies into these environmental trap, so you'll need to dedicate a decent amount of time to Lockdown in order to get this done. Once you achieve 100 Environmentalist medals, this achievement will unlock.