I think that's cool--couple things though.
The poke-power, Unown: Maybe there should be a catch, like there must be another unown in play to use it or something, searching your deck for an unown seems too easy. You might also want to change to: search deck or discard pile.
The attack: It would probably be better to something like this, though it is totally your call and i might be wrong:
Hidden power 40
Flip a coin for each energy attached to the defending pokemon. For each heads, this attack does 20 more damage. For each Tails, this attack does 10 less damage.
Again, your call, but this could i think make it better.