Grombas appear to have a rock for a head with a hole at its center for its eyes to see. It also has grass on top of its head and rocks for feet. In the game, they appear to have tendencies to trip while roaming. They don't often chase Mario and Luigi upon sight as much as the other enemies. Their dream-world counterpart is Dromba.
Grombas attack in two ways: After running up to Mario or Luigi they'll start tripping and roll towards them, or they'll dig out a rock with their feet and kick it towards the bros. Both attacks can be avoided and/or countered by jumping.