Rek'sai Volcanic Skin

Her back would be a molten volcano, and her tunnels would be lava pits. When she Ults to a tunnel it erupts and the more fury she builds the more lava starts flowing out of her back. Also burrowing would scorch the ground and cause lava to splash above the ground as well as when unburrowing. Moving while burrowing would leave a trail of flames that deal no damage of any kind, but look pretty cool. Her exoskeleton is obsidian and her more squish parts live mouth and unarmored joints would also be lava. I don't know it just makes sense to have an underground lava worm-thing.