Hey i just saw this on another forum and thought i'd bring it to the world of t-f.
Write a wish.
The next person to reply grants your wish, but there's a consequence to it...
(S)he then writes another wish, which the next person corrupts.
Example:
1st person: I wish I had X-Ray Vision.
2nd person: Granted, but it only works in nursing homes.
Here's mine.
I wish i could control time