This is an unusual champion, and very useful in defense against opponents who use artifacts and magic items. The base level of the Hydra in combat is the adjusted level of its opponent when first put into the battle. This means that a defending Lernaean Hydra will never play the first card into battle. While in the pool, the Hydra has no level, which is not the same as a level of zero (though it is counted as such for deck creation).

Cards that rely on affecting champions of a certain level do not affect this champion if it is not in combat with another champion, as it has no level to compare to the effect. For instance, the Spiderfell [BR-3] would force the player using the Hydra to discard a card, but since there is no opposing champion yet to provide a level, the Hydra is not discarded by the realm. The Hydra's immunities only take effect while in the pool, so it makes an excellent champion to attach potent magic items or artifacts to that shouldn't go into combat, like the Bag of Holding [AR-28], or the Throne of the Mountain God [4th-510].

The Lernean Hydra is not immune to cards while in combat, so cards like the Orb of Power [4th-170] are useful to make the Hydra a powerful champion in combat. If the Hydra goes into combat, gets a level, and then can't act (ala Time of Troubles [FR-99]), then the Hydra returns to his pool and another champion must be chosen.

If the Hydra enters a battle, has its base level determined, and for some reason (such as Time of Troubles being in play) cannot be in battle due to its level, the Hydra returns to its pool. Another champion may be selected for the battle.