Here is the full list of all 27 BUTCHER achievements.
Complete the game on "The Hardest" difficulty.
Beat The Last City.
Beat Volcano Research Station.
Die 200 times in total.
Beat Jungle Outpost.
Make 200 enemies die horribly by burning alive.
Kill 1000 enemies.
Repeat a single level 10 times.
Find 10 skulls.
Beat Old Military Base.
Beat Ironworks Facility.
Kill 10 enemies with a single railgun bullet.
Unlock new difficulty mode.
Find 20 skulls.
Find 30 skulls.
Find all skulls.
Complete the game on "Hard" difficulty.
Complete the game on "Harder" 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.
Maul 200 enemies to death with a sawspider.
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.