Death of the Dead.

Wanda is a uber nerd with the coordination of a seizure victim. Her karate trainer is an aging pervert with a penchant for ball gags and various sex toys. When a bus from a rival karate school accidentally runs over a couple scientists dumping a toxic chemical down the sewer, the entire class is turned into high flying, flesh eating baddies! As they wreak havoc on the town turning others into zombie ninjas, Wanda and her instructor must save the planet with the help of a magic karate belt.