Gambit

Yes, I know "“ Gambit is not a supervillain. Furthermore, when he first appeared alongside Wolverine in the Origins flick, he was disappointing. However, given his connection with Mister Sinister, he should cameo in the final Wolverine flick. And maybe, in this way, his solo movie would have another reason to exist.

In the comics, Gambit is hired by Sinister to retrieve some diaries from the Weapon X program. In exchange, Sinister would help Gambit with his powers.

Obviously, Gambit and Wolverine don't meet. And they shouldn't do it in the movie. However, even if in a credits scene, this would be great world building coming from Fox. And it would also be great fan service.

What other characters should be introduced in the final Wolverine flick? What other mutants, whether friends or foes, should be featured?