So as any comic fan is aware, magic exists. It is rather abundant, in fact, and generally breaks all of the laws of physics. Then again, it's magic. It can do that. Deadman can possess pretty much anyone, Zattana can create any spell by speaking backward, some characters can alter the very fabric of reality however they see fit.
Now, while Sentinels is rather open about the upper limit of a character's abilities, I'm going to put my foot down just a tiny bit on magic and how it functions. Now pay attention kids.
1. Characters with magical abilities cannot have any other powers.
This may seem rather...strict, however magic is extremely versatile. It's difficult to hold down without a substance similar to Nth Metal and it's almost impossible to limit effectively. So...I've just decided to handicap the rest of the character. Knowledge of the arcane and alike are perfectly fine however. These would likely come with the field.
2. Magic can easily be detected and traced.
By those so inclined, of course. A character who uses magic will often give off a magical aura in the Sentinels universe. This aura can be detected, searched out, and tracked. If someone wants to find a magic user, they may have to look hard, they may have to deal with a few wards and magical traps, but they'll find them. Eventually.
3. Magic cannot alter time, space, or reality.
This seems like a given in terms of balance, but in universe, magic follows a very strict set of guidelines. If you alter any of the previous three states of ethereal being, you break the laws of magic. Those who break the laws of magic face incredibly serious consequences by the powers that be, and more often than not their magic is just undone afterward. All of it. So sure, you can conjure up your fire and your water and your girlfriend because you wanted to give your hand a break, but once you mess with the laws of physics, the flow of time, or the laws of magic themselves, you open yourself up to a magical death penalty. End of story.
If your characters folllow all of these rules, you are free to have them, so long as the admins and mods approve of them.