Boulders are large rocks that would appear in several Mario games. They would usually act as obstacles for the player. They would make their first appearance in Wario Land: Super Mario Land 3 in the SS Tea Cup and Parsley Woods. They would return in Super Mario 64 in the Hazy Maze Cave, where they would endlessly roll in one of the rooms on a downward slope that leads to a bottomless pit. While Mario tried to climb the slope, the boulders would try to home in on Mario to knock him into the pit. In Super Mario 64 DS, Wario would be able to punch several boulders to receive a Power Star.
Boulders would appear in Super Mario Galaxy where they would roll around in various patterns and would knock down Mario if they hit him and make him lose a wedge of health. They would appear in several galaxies like the Good Egg Galaxy and could only be destroyed when Mario spins on the circular red area or be destroyed when Rainbow Mario runs into them.
In Super Mario Galaxy 2, they would be seen on the Boulder Bowl Galaxy alongside the Rock Mushroom. They could be destroyed by Rock Mario and this world would have a boss called Rollodillo who attacks in the same way as the Boulders do. He can only be defeated by Rock Mario. Sorbetti would use the same method of attack on the Freezy Flake Galaxy.
Boulders are set to appear in New Super Mario Bros. 2.