Veigars ultimate?
Maybe bring back the % mana dmg that would only proc if the target has no AP or barely any (less than 5 or 10% of your AP = mana dmg instead of 80% of AP)
So then he's only totally ineffective against AD energy/no cost champs instead of anyone who isn't AP.. Even a tanky AP can eat your burst a lot of the time.
I'm sure they would have to do some other tweaks (probably decrease AP% a bit) to make it work like anything else. I just feel late game he doesn't have as much presence as a snowballing type character should. When you compare him to the likes of Nasus anyways.