Denizen of the Deep

The drawback is the joke and the joke is the drawback. An 11/11 for eight mana was never going to be efficient, but the bounce-everything clause turns the card into a self-correcting trap: the bigger your board when this lands, the more you lose. Portal-era design ran on plain, swingy effects with no fine print to parse, and this leviathan is a pure distillation of "huge body, brutal catch." The detail that elevates it past comedy is that the clause is mandatory and untargeted (it returns each other creature you control, with no choice of which), so the rare builds that want it are doing so deliberately: a board stocked with enters-the-battlefield triggers can rebuy a fistful of them at once by sending the whole team home, then recasting it on the way back. The fantasy is the serpent surfacing and dragging your own fleet under with it, and the rules text commits to that fantasy without blinking. It is a creature whose own ability is the strongest argument against casting it, which is exactly why the players who do cast it are usually building around the punishment rather than enduring it.