Grrrol

Grrrols are spiked enemies that appear in New Super Mario Bros. U. They are similar to Spiky Tromp from Super Paper Mario, as they roll around trying to crush Mario, bouncing the walls and themselves. Grrrols are put on-screen by specific pipe-like walls which can make infinite units. These enemies resemble circular Thwomps with rolling red eyes and a big smile lacking one tooth. Like Thwomps, they are invincible, only being harmed by Invincible Mario.

The first appearance of Grrrols is in a secret room in Stoneslide Tower from Layer-Cake Desert. They are found again in a Rock-Candy Mines tower, Grinding-Stone Tower, where they are main obstacles. This level also presents Grrrol's larger counterpart Mega Grrrol. These feature a rather toothy grin with cheeks, which the smaller counterparts lack, though having the same traits.

Trivia

 * Grrrols and Mega Grrrols have similar faces to Bristles.
 * Their name is a pun on grrr, a sound made by similar species, Thwomps, and roll, their attack pattern.