Here is the full list of all 27 BUTCHER achievements.
Find all skulls.
Complete the game on "The Hardest" difficulty.
Complete the game in 45 minutes on at least HARD difficulty.
Complete the game on "Harder" difficulty.
Complete the game in 1 hour on at least HARD difficulty.
Find 30 skulls.
Impale 50 enemies on hook by kicking them.
Unlock new difficulty mode.
Find 20 skulls.
Die 200 times in total.
Impale 25 enemies on hook by kicking them.
Maul 200 enemies to death with a sawspider.
Kill 10 enemies with a single railgun bullet.
Complete the game on "Hard" difficulty.
Complete the game in 1.5 hour on at least HARD difficulty.
Beat The Last City.
Find 10 skulls.
Beat Volcano Research Station.
Beat Jungle Outpost.
Kill 1000 enemies.
Make 200 enemies die horribly by burning alive.
Beat Old Military Base.
Repeat a single level 10 times.
Upload your level pack to the Workshop.
Beat Ironworks Facility.