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Sub-Goombas are Goombas commanded by Private Goomp in Mario & Luigi: Dream Team. They appear during Mario's battle against the Elite Trio in Dreamy Driftwood Shore, where they are often used in the horde's attacks. The group of Sub-Goombas surrounding Private Goomp get resupplied by the line of Sub-Goombas in the background whenever any are defeated, and are the ones used in attacks.
The active Sub-Goomba horde may be ordered by Private Goomp to pile up into a rectangular formation, which is sent towards Mario to plough through him, although this can be countered and result in the Sub-Goombas taking damage. Sergeant Guy will turn the active horde into clones of him, who will all begin either attacking Mario with hammers or running past him harmlessly. If Mario hits any of the fake Sergeant Guys with a hammer when they get near, they will retain the damage sustained after the attack if they're not defeated as a result.
The Sub-Goombas also end up getting chased in the trio's group attack, and will try to escape from the giant Bob-omb Sergeant Guy carries much like Private Goomp. If Mario stomps any Sub-Goombas who try to escape by lining up with them and jumping, they will be stopped and prevented from escaping the future blast radius, taking damage when the Bob-omb goes off. Additionally, the Sub-Goombas horizontally lined up with Private Goomp and the front line of them in the background will take damage if Mario successfully counters Corporal Paraplonk's attack or in the case of Mario prematurely attacking the Sergeant Guy Cannon when refilled, the active Sub-Goomba horde.