Here is the full list of all 13 Sad Ghouls achievements.
Kill 20 or more enemies with a single shot
Get 1000 combo
Survive for 60 seconds without using the keyboard.
Force an enemy to die from unnatural causes
Survive for 500 seconds on the hardest difficulty
Survive for 28 waves on the hardest difficulty
Succumb to your own explosion
kill 2000 enemies in a single life
Find the hidden Sorg
Have less than 6 frames per second
with only one weapon equipped, get it to level 100
Get to wave 17 without jumping or dashing on the hardest difficulty
Kill a visiting wizard