You can beat the Hydra without actually killing the damned things by doing 20 face damage (I guess, I had a huge board and send one toon after the Baby Hydra and the rest face). You can still attack face with the send-all-to-face icon. All in all this one is way too easy since you can prevent the AI from doing anything by having enough blockers until you build a huge board.
Also a life-gain win of the final battle seems to prevent Amon from resurrecting. I'm guessing it'd be the same for hardcore.