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