Undead have rights, too!
Complete a level other than Astral Academy without directly killing any enemies

A quick and easy way to get this achievement is by using the wizard's summoning powers such as the box, plank, or any environmental object to kill (crush or smash) the enemies. I can confirm that the wizard's kills are not counted as direct kills, but this only works with the wizard. If you have to switch characters you can, but make sure you only kill with the wizard. The second level Astral Academy Hallways (level 2) is an easy level to get this achievement, and i would suggest you play the level on easy mode.

Good luck and I hope this helps you.