Here is the full list of all 14 Mr. Shifty achievements.
Beat the game
Finish act 2
Finish act 1
Punch 1000 times
Punch a guy out a window
Stick a mine to an enemy
20 enemies die from friendly fire
Hit an enemy with a door
Kill over 836 enemies
Complete a stage with 0 deaths
Complete all stages with 0 deaths
Beat the dev's best speedrun time 1:19:21
Pin 5 enemies to a wall with the trident
Kill 6 enemies in a single slowmo