The ability to alter my height, retaining all of my real sized attributes (I guess it would have to be magic, then), leaving me, potentially, as an inch high dude who can lift stuff hundreds of times larger than myself. Too super? Well, what if this power only worked when I was in my bedroom? Now, that's fairly useless, and cool as hell. Like screwing around in the ship in Metroid Prime: Corruption.
Yeah, I came up with that power when I was seven, and playing kid games with the girl who lived in my complex. Thanks for bringing up those memories.