I just had this idea last night for a terrible spell - Abomination. Cast on a pregnant woman or other mammal, it causes the target to give birth at the end of its pregnancy term to a horribly misshapen monstrosity.
Possible outcomes for human targets:
- Snake with human intelligence
- Two-headed snake
- Two-headed human
- Human with snakes growing out of his shoulders
The abomination born, if it lives, is unnaturally strong, savage, and often, anthropophagous. Most such births however will be stillbirths.