Hydra wants moar...

Fast Healing later (ridiculous at level 1), give combat reflexes at some point (and have it work the way it normally does for hydras.), hand it the pyro or cryo breath weapon, and at some point you need to specify that the hydra actually gains more heads... right now, the creature has one (RAW) and just attacks really fast.

I might be missing something, but that's what I see.