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