Here is the full list of all 20 Void Prison achievements.
Don't dash for a minute
Don't get hit for a minute
Survive 30 seconds
Survive for a minute
Survive for 2 minutes
Survive for 3 minutes
Survive for 4 minutes
Survive for 5 minutes
Survive 2 minutes without powerups
Get hit 50 times in one round
Kill 1000 bats
Kill 1000 mages
Kill 1000 moles
Kill 1000 runners
Kill 1000 shroomers
Kill 1000 skeletons
Kill 1000 slimes
Kill 1000 shooters
Kill 1000 tanks
Kill 1000 worms