The ability to enter and manipulate dreams. I promise I won't steal your secrets or manipulate you into doing what I want in the waking world like in Inception. I'd rather psychoanalyze you. Then I'll steal your secrets. I may or may not lead you to insanity after that though...
A tweaked version of the Doctor's regeneration. By tweaked, I mean no regen limit (I believe he's only limited to 12? I've been so out of touch with the fandom lately). So I can't choose what I look like when my current body takes too much damage/dies, but that's the thrill of regeneration! I would be that sort of immortal that would take on different identities with every regeneration.
Note: My appearance when I enter the dreams does not necessarily have to be the same with my physical form. So the regeneration ability does not apply there. Plus, I can't die in a person's subconscious, since I'm controlling the subconscious!
Dimension hopping. I may not be able to create, destroy or manipulate realities (I've already got my create, destroy and manipulate urges covered with the dream manipulation), but I'll be able to visit some of them, maybe even live in them!
I'd be the ultimate regenerating, dimension-hopping, dream psychoanalyst/thief tourist ever!