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Complete all 17 levels on Apocalyptic difficulty.

Apocalyptic difficulty will not be available until you complete the game on any other difficulty first. I would suggest just leaving the game on Normal your first playthrough, then going straight to Apocalyptic next. The difficulty achievement for Hard will stack along with this. To change the difficulty, press [ Register or Signin to view external links. ] on the mission select screen when inside The Void. Run through all 16 levels a second time on Apocalyptic, and complete the secret Killington fight which is locked to this difficulty (see "Wicked Killington") to earn this achievement.

Since you should have completed all the other miscellaneous achievements/quests in the first playthrough, you can just focus on the main mission objectives and only fight the necessary enemies. Be sure to always use executions when you are surrounded by enemies as this protects you from damage and has a small AOE which will damage other enemies and possibly set up more executions. For all encounters, use Strife and keep your distance, use clones when surrounded, and don't forget about your potions! There are plenty of checkpoints in the game though, so dying really doesn't set you back much at all.

With how the game's leveling system works, where to best put your Creature Cores can be a bit confusing. I found the build below to be extremely helpful, while this one was good as well. I personally started this run at ~1200 gear score and ended at ~1400 so don't be put off by the suggested 1900 on the mission screen. I think the max you can even get is around 1600 anyway. I didn't collect every armor piece for either character, so the two extra core slots (where Leviathan and Moloch are in the build below) were not available to me but it didn't seem to matter much.

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