You post whatever super power you want but the next person gets to name the conditions on how you can/can't use the powers. For example:
Person A: I want Super Speed
Person B: Your power is null if you have to use the bathroom really badly.
The condition cannot completely negate the power either. So you cant say you only have super speed when you're asleep or when everyone in a 10 mile radius is looking north while sneezing.
I guess I will start.
I would want the ability to shape shift into anyone I want.