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