Here is the full list of all 21 Radio Viscera achievements.
Find every safety poster
Find all Observation Stations
Unlock all Mutators
Collect 666 skulls
Combine 2 or more Mutators
Finish a level with no damage taken
Keep one action combo going for a whole level
Collect every skull in a level
Kill an enemy via a bouncy rebound
Kill an enemy after they pass through a pane of glass
Hitch a ride upstairs
Activate a laser that kills an enemy in mid-air
Ride a reel-to-reel
Get crushed by a light pole
Smash every door in a level off its hinges
Destroy the Lawn Aerator
Destroy Burt Casserole
Escape into the hills
Turn the music volume all the way down
Play with the lowest quality settings
Skip the splash logos