Here is the full list of all 27 BUTCHER achievements.
Beat Jungle Outpost.
Die 200 times in total.
Impale 50 enemies on hook by kicking them.
Kill 10 enemies with a single railgun bullet.
Maul 200 enemies to death with a sawspider.
Impale 25 enemies on hook by kicking them.
Repeat a single level 10 times.
Kill 1000 enemies.
Make 200 enemies die horribly by burning alive.
Beat Old Military Base.
Beat Ironworks Facility.
Unlock new difficulty mode.
Find 10 skulls.
Find 20 skulls.
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.
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.