I'd be a Ditto, just so I could freak people out all of the time. If I were near some Water Pokemon, I'd be able to go under the sea; If I were near some Flying critters, I'd be able to soar through the skies etc. I'd make sure not to antagonise anyone, though, as Ditto isn't the strongest of critters, after all. That's the curse that comes with gimmicky Pokemon, unfortunately.