2020-11-10 : Even though the player who was dealt damage chooses the target for Bladegriff Prototype's ability, you are the controller of the ability.

2020-11-10 : 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.