Boulder

Boulders, also referred to as Rolling Boulders, are large rocks found throughout various Mario games, usually serving as obstacles.

Super Mario World
Boulders first appear in Super Mario World, where they are dug up by Diggin' Chucks as a form of attack. They continuously bounce on the ground in one direction (turning the other way when they bump into a wall) until they are hit by Cape Mario's attack or sink into lava.

Super Mario Land 2: 6 Golden Coins
In Super Mario Land 2: 6 Golden Coins, they are dug up by Gorontos and act the same as in Super Mario World.

Super Mario 64 / Super Mario 64 DS
Boulders also appear in Super Mario 64 and Super Mario 64 DS within the course the Hazy Maze Cave. They are found in a large area, endlessly rolling down a slope and then falling into a pit. If Mario, Yoshi, Luigi, or Wario tries to climb the slope, the boulders deliberately roll in his direction, so he has to dodge them. The Hazy Maze Cave has a mission called Watch for Rolling Rocks, where the goal is for Mario to avoid the boulders and grab the Power Star on a nearby corner. In Super Mario 64 DS, the Power Star is obtained differently: Mario, Luigi, or Wario must grow from a mushroom and break three or four boulders to reveal the Power Star. Alternatively, Wario can break the boulders by punching them. Also, in the DS version of the mission Swimming Beast in the Cavern, Wario must punch a boulder on the island in the center of the Underground Lake to reveal a Power Star.

Super Mario Galaxy
In Super Mario Galaxy, Ruby Rocks roll on open or closed circuits, coming out infinitely out of tunnels in the former case and falling into an abyss afterwards. If Mario touches them, he is knocked away and loses one wedge of his Health Meter. Ruby Rocks are semi-common obstacles that appear in several galaxies, including the Good Egg Galaxy and the Honeyhive Galaxy. They can be destroyed if Mario spins their weak spot, a circular red area. They can also be destroyed if Rainbow Mario collides with them, a rubbery bulb is knocked into them, or if the second player uses their Star Cursor to hold one in place, allowing a second Ruby Rock to collide with it, destroying both Ruby Rocks. Upon destruction, Ruby Rocks leave a large amount of Star Bits. Ruby Rocks in this game have some subtle size differentiation in different levels, though one in the underground section of the Dusty Dune Galaxy is especially large.

Super Mario Galaxy 2
In Super Mario Galaxy 2, boulders reappear in the Boulder Bowl Galaxy, a galaxy which is appropriately centered around boulders, as well as the Rock Mushroom. This time, the boulders can also be destroyed by Rock Mario. The boss of this galaxy, Rollodillo, attacks in the same way as a Boulder, and can only be defeated by using Rock Mario. Sorbetti, the boss of the Freezy Flake Galaxy, also uses a similar strategy during the boss battle.

New Super Mario Bros. 2
Boulders make their next sidescroller appearance in New Super Mario Bros. 2. They appear in World 3-5, which is an underwater level. They are common obstacles here but they are also necessary to obtain several Star Coins as they are enclosed in blocks that cannot be broken by Mario. Boulders can be destroyed using a Super Star, an Invincibility Leaf, or a Gold Flower.

Super Mario Odyssey
Boulders appear again in Super Mario Odyssey. One specific boulder that takes the form of a large, oblong rock is found in front of a tree in the Deep Woods in the Wooded Kingdom and can be captured, which allows it to be moved to reveal a tunnel containing a Power Moon. Many rolling boulders also appear in the Underground Moon Caverns in the Moon Kingdom and in the segment where Mario captures Bowser in the cave on the Darker Side of the moon. These round boulders can be destroyed by ramming into them as a Chargin' Chuck or by clawing them as Bowser, and may produce a heart in the latter case. Additionally, during the first battle against Bowser in the Cloud Kingdom, Bowser occasionally attacks Mario by throwing brick-like boulders at him (the second battle in the Moon Kingdom replaces the brick boulders with burning Bowser shells), and many boulders fall down at the end of the game when Mario captures Bowser in the Moon Kingdom as the caves collapse, serving as obstacles, with yellow markers appearing where they are set to land.

Mario Kart 64
Boulders make their first Mario Kart appearance in Mario Kart 64, where they appear as obstacles in Choco Mountain. When the player is hit by a boulder, they will be flattened.

Mario Kart: Double Dash!!
Boulders return in Mario Kart: Double Dash!! as obstacles in DK Mountain.

Mario Kart DS
In Mario Kart DS, boulders return in Choco Mountain, which is a classic course in this game. Large pinballs similar to boulders appear in Waluigi Pinball.

Mario Kart Wii
Boulders reappear once more in Mario Kart Wii in DK Mountain, which appears as a retro course.

Mario Kart 7
In Mario Kart 7, boulders make yet another appearance as obstacles in Rock Rock Mountain and Maka Wuhu towards the end of the track. Starting from this game, boulders no longer cause the player to be flattened when hit. Instead, the player will spin out.

Mario Kart 8 / Mario Kart 8 Deluxe
Boulders appear in Mario Kart 8 and its enhanced port, Mario Kart 8 Deluxe, as an obstacle in Bowser's Castle. They resemble their Super Mario Galaxy counterparts in texture, but without the red jeweled side. Millstones similar to boulders appear in Thwomp Ruins. Boulders also appear in N64 Choco Mountain in the Booster Course Pass for Mario Kart 8 Deluxe.

Mario Kart Tour
Rolling rocks reappear in Mario Kart Tour as obstacles in 3DS Rock Rock Mountain and N64 Choco Mountain. The player can get points by hitting rolling rocks while invincible.

Mario Party series
Boulders appear in some minigames in the Mario Party series. In Boulder Ball in Mario Party 3 and Mario Party Superstars, the solo player must use a machine to fling boulders at the team players to prevent them from reaching the top of a slope. In Granite Getaway in Mario Party 6, the players need to run away from a giant rolling boulder. In Rocky Road in Mario Party 6, Mario Party: The Top 100, and Mario Party Superstars, teams need to punch and kick boulders blocking the road to destroy them so they can reach the finish line. In Block and Roll in Mario Party 9, the rivals must roll boulders down to the solo player to prevent them from transporting three blocks from one side to the other.

Donkey Kong Land
Boulders are present as obstacles in Mountain Mayhem and Landslide Leap, two levels from Donkey Kong Land. They periodically fall down from holes in the background wall, bouncing briefly on any platform they fall onto. They will damage the Kongs upon contact and are completely indestructible, even against Rambi the Rhino.

Donkey Kong 64
"Can pick up a boulder with relative ease. Makes crushing rocks seem such a breeze!"

- DK Rap

In Donkey Kong 64, boulders appear as stationary obstacles, often appearing on various pads, which require them to be moved before the pads could be used. However, only Chunky Kong can lift them. Boulders also serve as weights, and are sometimes needed to keep various switches pressed down. In this game, they are dark green in color.

Donkey Kong Jungle Beat
Rolling boulders are present in Donkey Kong Jungle Beat, first appearing in Massive Canyon. They can only be jumped over in this game.

DK: Jungle Climber
Boulders also appear in some cave levels of DK: Jungle Climber, starting in Cool Cool Cave. These boulders have many pegs on them, and Donkey Kong can spin the boulder either left or right, based on which side he is spinning from it. Boulders are required for reaching high areas, including peg boards or ledges.

Donkey Kong Country Returns
Boulders of various sizes appear in Donkey Kong Country Returns, primarily in Boulder Roller. Most of them are covered in spikes.

Wario Land II
In Wario Land II, boulders fall from holes in the walls of underground areas, appearing only in Avoid the rocks! and The Final Battle!!. Small ones can be held and thrown to defeat enemies or Enemy Blocks, and large ones squash Wario into Flat Wario.

Wario Land 3
In Wario Land 3, small boulders only appear in the late-game stage, Above the Clouds, working as they did in Wario Land II. However, they now have a new sprite, being more lumpy than before.

Wario Land 4
In Wario Land 4, Iwao produce boulders from the ground and throw them at Wario to attack him. These boulders roll on the ground until they hit a wall or fall into lava and will damage Wario if they hit him. They cannot be destroyed, only avoided. There are also small, holdable boulders from the previous games, working as before, that appear in several levels.

Wario Land: Shake It!
In Wario Land: Shake It!, boulders appear as obstacles in volcano-related courses. In Mt. Lava Lava, there are enormous boulders held in place either by Hard Blocks or Bomb Blocks. When Wario destroys these, the boulders immediately start chasing him down a path, destroying every enemy and block in its path. If a boulder catches up to Wario, he will remain stuck to its surface and move along with it until the boulder stops somewhere and flings Wario forward due to the momentum. In Sneak Peak, there are small boulders that can also pick up Wario as they roll, but can be jumped on to reach a higher area. They endlessly come out of openings in walls and roll on the ground until they fall into lava.

Wario: Master of Disguise
In Wario: Master of Disguise, boulders are generated by Poobah the Pharaoh from his nostrils as part of his first attack phase. When they land on the ground, they remain still for a moment before rolling towards Wario, breaking when they hit a wall. Boulders can hurt Wario if touched from the sides, but can be destroyed with a jump.

Yoshi Topsy-Turvy
In Yoshi Topsy-Turvy, boulders have three indentations similar to a bowling ball. Yoshi can stand on boulder. The player can tilt the Game Boy Advance to roll it. While it is rolling, it can defeat enemies.

Trivia

 * During the first part of the final Bowser battle in Super Mario Galaxy, one of Bowser's attacks involves surrounding himself with rock fragments and rolling around the planet much like a Boulder in an attempt to squash Mario. Bowser's head sticks out of the rock in the same area where the red spot would be on an actual Boulder. Mario must spin Bowser's head to break him out of his rock shell.
 * In Super Mario Galaxy 2, the Rock Mushroom is introduced for the first time. When collected, this power-up allows Mario to transform into Rock Mario, taking the form of a round Boulder-like object, and roll into obstacles and enemies, much like Bowser did in Super Mario Galaxy's final battle. Mario's head sticks out of the rock where the red spot is normally on a regular boulder.