Superhuman strength and speed, nigh-invulnerability, accelerated healing factor, flight, enhanced vision and hearing, telepathy, and the ability to perceive mutants' auras.
Is Cassie resistant to Telepathy? M is very skilled in that regard.
I'm not sure M's strength/speed/durability has been shown to be on the Wonder Girl's level, but then i'm not that sure what level Wonder Girl is on in the first place.
If this is a no prep fight. I would have to give it to M 6 out of 10 times. WonderGirl is a warrior, she is going to be tough when she comes of age. But M has way to many powers. By the way which version of M. do all versions have the same powers?
^ My first introduction to M was through early Generation X also. She seems to be much stronger, faster and more adept at telepathy currently in X-Factor.