You can only find them in the Death school line of spells, and it's still one of my favorite things about my chosen class . . . health drain spells! From the first time I cast a Ghoul as a baby necro to just last night when I hit a mob with Dr. Von's Monster, It's a totally awesome thing about Wizard101.
It finishes off a mob and it makes sure you're at full health for the next battle.
I can't express how much that helps play this game. Overpowered? Maybe, but if it brings the happy, it brings the happy, and it's definitely an awesome spell mechanic in Wizard101.