Face the Hydra is a special game with special rules which can be found here.
I know that a spell that deals direct damage to a player cast on the hydra will deal the damage to one of its head. The same applies to trample damage, and so ons, for damages.
But is the hydra considered a player?
For instance, I have a creature that gets +1/+1 counters each time it deals damage to a player. Would that ever be triggered since you attack its heads directly? What if that creature was unblockable?