I would have to recommend the Halfling Jinx Witch.
Jinx is an alternate racial trait that swaps the Halfling's inherent luck bonus to saves for the ability to inflict a minor debuff on an enemy.
You will be solid at debuffing all the way through your career with Hex only, and still have an excellent selection of spells to boot. But with the above combination, at level 9 you can Evil Eye for a total of -7 to all saves. Throw in a Quickened Ill Omen for funsies in the same round and then the next save they make has those massive penalties and they need to roll twice and take the worst result.
After that it's just about which variety of murder you want to inflict on them.
If you really wanted to go crazy you could also throw in Sluggish Jinx to have -3 penalty apply to attack rolls and initiative if you'd like.