Encounter
Treachery

When Revealed: Each Hydra minion engaged with a hero makes an attack against that hero. Each player who was not attacked this way searches the encounter deck and discard pile for a Hydra minion, puts it into play engaged with them, and shuffles the encounter deck.

Boost:
The Rise of Red Skull #147. Hydra Assault #6.
Hail Hydra!
Reviews

Should read: “When Revealed: Each Hydra minion engaged with a hero attacks that hero. Each player who was not attacked this way searches the encounter deck and discard pile for a Hydra minion and puts it into play engaged with them. Shuffle the encounter deck if it was searched.” (Changed the shuffle ability to only occur if the encounter deck is searched.)

Put in the RulesReference

Freakmod · 103