Micro-Goombas , also known as "Mini goombas", are tiny, infantile Goombas.
Super Mario Bros 3
In Super Mario Bros. 3, Paragoombas would drop them on Mario and they would swarm over him, impeding his movement and jumping ability. Mario could shake them off if he struggled hard enough.
In 3D games
In their 3D appearances, Micro-Goombas behave just like normal Goombas, but they are smaller and slower. They will charge toward Mario when they spot him, but can be easily defeated by jumping on them or punching them.