Bad luck, there.
Anyway, if Pythium has Serpent Priests, he's playing Serpent Cult. You probably won't have much to worry about, as Hydras are just a little worse than Mammoths routing, and your archers should be able to cause a rout before they get to you. Unless they're like me and play with Berserking Hydras...
As long as you have your High Seraphs and they can at least cast Thunder Strike (or whatever it is) or Orb Lightning, I really don't think you'll have much to worry about. High Seraph vs. Ulm -> Sauron vs. Dunedain... piles of men flying everywhere.
Keep up the good work.
Bayushi Tasogare