You can't have the theme music from Paddington Bear, because that's already Paddington Bear's theme music. He has dibs on it.
Paddington's special power is that he is 3D in a world that is otherwise entirely 2D. Being 3D might not sound that cool to you, but it seems to make people think shit films are great; and if you met someone who existed in four dimensions and was perpetually rotating onto their own mirror image, as well as producing marmalade sandwiches from their hat, you'd be pretty damn impressed.
So you can pick anything that isn't already someone else's theme music; like God Hates Us All by Slayer, for example. Of course you don't want that, it's just an example. Pick your theme music and the rest will follow.
I'm going to go for Rock 'n' Roll Pumpkin by Green Jellÿ.
I figure my special power is going to be something along the lines of driving around real fast, leaning out of the window with my head on fire.
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...and then I went to a party at Casa del RoboJew where we did maths for two hours and everyone else got drunk and mocked us. It's good to have him back.