Grrrol

Grrrols are spiked stone enemies first appearing in New Super Mario Bros. U. They are similar to Spiked Balls and Spiky Tromps from Super Paper Mario, as they roll around trying to crush Mario, bouncing off the walls, themselves, and other solid objects. These enemies resemble circular Thwomps with rolling red eyes and a big grin with one tooth missing. The spikes they are surrounded by subtly alternate between lighter and darker shades of grey. Like Thwomps, they are invincible enemies, and only the Super Star has an effect on them, as does hitting the Item or Brick Block they are on from below, making them slightly weaker than Spiked Balls. Grrrols are spawned by specific pipe-like walls, which can make infinite units. They can also defeat any enemy they roll into.

Grrrols first appear in a secret room in the Stoneslide Tower of Layer-Cake Desert. They are found again in the Rock-Candy Mines tower, Grinding-Stone Tower, where they are the main obstacles. This level also introduces the Grrrol's larger counterpart, Dai Gorō.

The Grrrols return in New Super Luigi U, appearing in the Layer-Cake Desert stage Underground Grrrols as the main obstacles. They also appear in Stone-Snake Tower of Soda Jungle.

Grrrols reappear in Mario Party 10 as obstacles in the minigame Hop, Drop, and Roll.

Trivia

 * Their name is a pun on grrr, a growling sound, and roll, their attack pattern.