Ryan Reynolds = Leprechaun
Ryan Reynolds was a leprechaun. Here is the proof:
1) He appears right after a magical rainbow.
2) He befriends Gerry immediately and stays with him for no good reason.
3) He brings Gerry good fortune as long as Gerry follows his lead (Reynolds is literally incapable of making a losing bet, but when Gerry "turns his back" on him and tries his own luck, he has no more luck than a mere mortal.
I must not be the only one who came to this conclusion.