Sumo Brothers are a sub-species of Hammer Brothers who first appeared in Super Mario World. They act more or less the same way in Mushroom Kingdom Fusion.
In that game, Sumo Bros. are large and orange in color and wear black shells. They also have a spike on top of their head, meaning Mario will injure himself if he jumps on one. Sumo Brothers would stand on top of blocks and attack Mario by stomping their foot, which will cause a spark to drop below; this spark will ignite when it hits the ground, making a wall of fire. Sumo Bros. could only be defeated by throwing a Shell at them, by hitting them with a Cape as Cape Mario or by touching them with Mario when he is powered-up by a Starman. Hitting the block they are standing on from below also works, but is more difficult than other ways due to the fires caused by their lightning-stomp attack.