[Ylvali]

I tested some blessings. Most sucessful so far is, surprisingly, Air 6 astral 10. Protects agains arrows and cavalry charges as well as giving them MR 18, Which would be great in late game. Also a very useful pretender.

I tried fire thinking it would work well with all those heads, but it seems to even out because they lose their heads faster. F9 S9 could work but is hard to afford.

Water meakes them quick but also tired, and they still lose heads quickly which kind of ruins the extra attacks(like with fire)

Earth 9 didn´t do much for them but earth 4 could be worth it.

S9, D9 makes them fantastic SC killers. All those AN attacks with raised affliction chance. Would also make a great late game pretender. Hard to afford though.

I think my final choice would be: A5S9E4, A6S10 or S9D9

Edit: I´d like to add that fairy queens are great hydra buffers. They can:

Cast wind guide and later on fog warriors out of the box. Fog warriors is awesome with regeneration.
Heal your hydras afflictions, which could actually be worthwhile sometimes.
Easily be deployed through both flight and cloud trapeze.
Refill your ranks with wine ogres (or fairys if you don´have a lab there, those can fly to the rear and annoy archers so your hydras dont get shot at)