In his first debut, Goombs appears to be a smaller, otherwise regular Goomba. However, when he returns in Super Mario Bloopers: SECRET LIFE OF GOOMBAS, his face always appears with a smile, which he claims to have happened due to going through puberty.
Goombs is depicted as being a normally friendly child, although he appears to be easily startled, such as when he first meets Mario and fears that the plumber might eat him and Bobby. However, Goombs does prove to care deeply about his friends, going so far as to bust Mario out of prison, even if it meant betraying his entire village.
Goombs also mentions that he enjoys collecting and playing with Barbie dolls; though it is unknown whether or not he ever grew out of this hobby.