The Fire Sumo, more appropriately known as the Sumo Brother, is often featured in poops starring Mama Luigi and Yoshi. Almost always, it stomps the ground, causing a giant crack in the earth. Mama Luigi then falls into the earth over a river of lava. Usually everything that happens after that is different according to the pooper who created the work.
The immediate presence of a Fire Sumo causes the buttocks of present members to glare undeniably through their clothing.
If you ever encounter a Fire Sumo in the real world, run away immediately. If you don't, it will make you fall down a crack straight into Hell.