@never give up: If Mystique has prep she could win in Round 3, and also by shape shifting she can trick the Predator but it will be hard considering the fact that the Predator has technology that tracks heat, however Mystique is very cunning as well as a fast thinker so she can hide and orchestrate her next plan to take down the Predator.
Unless Mystique is stronger than I remember, Predator should have all three.
This. Raven did show some impressive skill in H2H but Predator is too strong for her skill to really matter. The movie version doesn't have weapons so while I think her shape-shifting can help to some degree with stealth attacks but I really don't see a way for her to really do major damage.