Siren

The Siren is a Forgotten Minion that can be summoned by merging a max level Banshee and Ghoul when the Ancient Tablet allows. Its effect is to summon a random Champion that is not currently in the lair.

(Tip: to guarantee a desired champion summon, even a Protector, have all 5 other champions in the lair at the same time before activating the Siren's summon.)