Here is the full list of all 27 BUTCHER achievements.
Unlock new difficulty mode.
Find 20 skulls.
Beat Jungle Outpost.
Die 200 times in total.
Find 10 skulls.
Beat Old Military Base.
Maul 200 enemies to death with a sawspider.
Beat Ironworks Facility.
Kill 1000 enemies.
Repeat a single level 10 times.
Make 200 enemies die horribly by burning alive.
Kill 10 enemies with a single railgun bullet.
Find 30 skulls.
Find all skulls.
Beat Volcano Research Station.
Beat The Last City.
Complete the game on "Hard" difficulty.
Complete the game on "Harder" difficulty.
Complete the game on "The Hardest" difficulty.
Complete the game in 1 hour on at least HARD difficulty.
Impale 25 enemies on hook by kicking them.
Impale 50 enemies on hook by kicking them.
Complete the game in 45 minutes on at least HARD difficulty.
Complete the game in 1.5 hour on at least HARD difficulty.
Upload your level pack to the Workshop.