Coral Tombs in Heroes of Ruin likely a mini boss.
Lurking in the dark depths of the Coral Tombs of Agmera this monstrosity combines the head and predator instinct of a massive shark with the tentacles and cold intellect of a giant octopus. The Hellmouth is an artificial creature conjured by a mind that sought to create the ultimate biological weapon. But like all mad ideas the Hellmouth was more successful and deadly than anyone could imagine. The resulting creature was too cunning to be controlled and too ferocious to be contained. The beast roams free devouring anything unfortunate enough to cross its path.
The Hellmouth is an apex predator. It has no fear of any creature, living or undead. Its massive size makes it capable of intimidating even the most capable of adventurers. The creature can sustain itself equally well on land or underwater. One of its preferred tactics is to wait submerged in a pool of water that leads to the ocean and pounce onto land to consume its victim. The Hellmouth typically uses its enormous tentacles to bash its prey into a pulp. Once the victim has been sufficiently bloodied, it uses its razor sharp teeth to deliver the finishing blow.
Only having surfaced in the last year, reports of it are scarce, since those who cross its path rarely live to tell the tale. The myth of the Hellmouth is passed between buccaneers and corsairs in sketchy taverns over a tankard of bitter. Sailors report glimpses of the beast and the shimmering shadows of their comrades being ripped apart limb from limb. Wherever the creature came from, it's clear that even the pirates of the Coral Tombs want nothing to do with it.
If anyone could make an accurate study of the beast, it would've been Eckhardt, a prestigious wizard who specialized in the magic relating to living creatures. However, the mage hasn't been seen for several months. Close associates of Eckhardt know that the mage kept a remote laboratory at the Coral Tombs and secretly feared the Hellmouth may have had something to do with Eckhardt's disappearance.