The pyrohydra is a hulking serpent of pure magma with a dozen flailing heads. Born of divine elemental power, this living pyroclastic floe leaves a trail of oozing, burning destruction wherever it moves. Its heads are amorphous extensions of its own elemental nature. Like other hydras, it can grow more heads whenever one of its existing heads is destroyed—however, it can also channel its own elemental life force into creating new heads. More frightful still, it can destroy its own heads to create an eruption of magma and toxic gas, burying all nearby in molten rock.
Pyrohydras were first brought into being by Imix, fiery prince of Elemental Evil, who used them to guard his domain on the Elemental Plane of Fire. Since their first creation, pyrohydras have become apex predators of the molten, flaming seas of the Plane of Fire—and have occasionally emerged into the Material Plane, sometimes called by Vanifer’s Cult of the Eternal Flame, sometimes emerging through natural planar rifts. On the Material Plane, pyrohydras frequently lair in natural volcanos, but they also makes lairs in ancient forests, and take great joy watching the world around them burn to cinders. When creating a pyrohydra lair, consider using the Volcano Temple map or Forest Shrine map from Mythic Odysseys of Theros, or the Weeping Colossus from Princes of the Apocalypse as a starting point.
  These elemental behemoths possess brutish intelligence, and delight in appearing to mortals as demigods and demanding their worship. They have little use for material tribute, for such gifts simply melt in their molten bodies, but living sacrifices entertain them greatly.