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