Flying
Whenever Bladegriff Prototype deals combat damage to a player, destroy target nonland permanent of that player's choice that one of your opponents controls.
Even though the player who was dealt damage chooses the target for Bladegriff Prototype's ability, you are the controller of the ability.
If an opponent dealt damage by Bladegriff Prototype leaves the game before the triggered ability goes on the stack (most likely because that player's life total was reduced to 0 or less in combat), you choose another opponent to choose the target permanent.