What kind of powers does Mages and Seers have for combat. I know they're not for combat like a Knight or Prince or something like that. But both Rose and Terezi kick ass in [S] Collide. So they should have something, no?

First of all, foresight of ANY kind during a combat is overpowered. To know what your enemy is going to do, where they’re going to be, immediately allows for you to counter the attack before they can even start it. If a Seer is proficient at combat, they can absolutely wreck. Remember, if you Know, you can Change the outcome, just based on that new knowledge you gained. Adding on top of that, Aspect Majyyks are completely possible- See Rose’s Light Magic. She’s a Seer, but she can cast light beams and spells. So there’s not really anything truly ‘non-combat’ when it comes to Classes, same way there’s not Classes that are ‘only combat’.