Inactive lava zone

Deep down at the bottom of the world this biome rests, its very open, lots a lava, lava pouring from the ceiling, lava coming out of walls and lava everywhere on the ground, this is basically the overworlds version of the nether. a new mob called the inferno from a mob update spawns there, and possibly a new structure. This biome would only fit if there was an extra 84-80 blocks before you hit bedrock. Sometimes you might find an entrance to a cave where you find a new ore. And if volcanoes are ever added, then digging down near one can lead you to safe entrance into the lava zone.