i would either want invisibility, or i would want to be ability to be super aware of my surroundings, if you have ever seen the Bourne ultimatum, supremacy, or identity this is where i got the idea from he is always so aware of his surroundings and it was practically unnatural
1) magic!!! 2) invisibility at will 3) stop time 4) duplicating myself so i could be in two places at once 5) flight 6) shape shift 7) going into the pages of a book and living the adventure as one of the characters or something. especially if i read the book first, then i could tell Harry Potter where the horcruxes were =]
I think being able to read peoples minds and make them hear and see stuff that they're not really hearing or seeing. Lol, id be freaking everybody out, making them see demons or speaking complete jiberish in their heads.