EXTRA: Chaos Malachite Achievement in Vampire Survivors

Refer to EXTRA: Bat Country (10G) to first unlock the extra stage, Bat Country. With it unlocked, start up a run with your best character. There's nothing really difficult about this stage at all, since it's just different forms of bats. Use your usual tactics to survive. Feel free to turn on Hurry mode to speed this up, since it's a pretty easy stage.

At the 9-minute and then 18-minute mark, a green arrow will pop up on screen pointing you to a new item that spawned. Follow the arrow to a little glowing item and pick it up. You'll get Apoplexy at 9 minutes and Chaos Malachite at 18 minutes. There aren't any bosses in this stage or anything else to do, disappointingly, so once you collect Chaos Malachite at 18 minutes, quit out of your run to unlock both achievements.