Hydra Rules

[Twowolves]

I feel the one AoO per opportunity, with lots of AoOs to take is more in line with the majority of other CR4s, using the 5 headed hydra for example.

I agree completely here, but again, I think I'm in the minority.

Also, I'd like to think the breath weapon damage is 3d6 per head, not 3X(# of heads) d6. A 5 headed pyrohydra is what, CR 6? 15d6 breath weapon plus fast heal 15 and 5 attacks per AoO seems a little much for CR 6, and it just gets worse from there.