Here is the full list of all 16 Graveyard Shift achievements.
Score a 1000
Score a 100
Complete game in hard mode
Kill 500 ghosts
Collect 1000 mushrooms
Throw 100 mushrooms
Complete game in easy mode
Kill 250 ghosts
Collect 500 mushrooms
Collect 250 mushrooms
Kill 100 ghosts
Kill three ghosts with one mushroom
Complete game in normal mode
Score a 10000
Throw 500 mushrooms