Boulder

Boulders are large rocks found throughout various Mario games, which usually serve 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
They also appear in Super Mario 64 in Hazy Maze Cave. In one room, boulders endlessly roll down a slope and into a bottomless pit. If Mario attempts to climb the slope, the boulders deliberately try to home in on him, although they can be dodged. The level's sixth Power Star is entitled "Watch for Rolling Rocks," and is located near the Boulders. In Super Mario 64 DS, Wario must instead punch several boulders, (or ram them upon growing with a Super Mushroom) to receive the Power Star.

Super Mario Galaxy
In Super Mario Galaxy, boulders 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. Boulders 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 boulder to collide with it, destroying both boulders. Upon destruction, boulders leave a large amount of Star Bits. Boulders 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 appears in the Wooded Kingdom, taking the form of a large oblong rock that can be captured by Cappy and slowly moved to make way to an entrance. Many rolling boulders also appear during the platforming part where Mario captures Bowser in the Moon Kingdom as well as an optional area 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, although they do not produce any items. Additionally, during the first battle against Bowser in the Cloud Kingdom, Bowser would occasionally attack Mario by throwing brick-like boulders at him (the second battle in the Moon Kingdom replaces the brick boulders with burning Bowser shells).

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
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.

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.

Mario Kart 64
Boulders make their first Mario Kart appearance in Mario Kart 64, where they appear as obstacles in Choco Mountain.

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

Mario Kart DS
In Mario Kart DS, Boulders appear again in Choco Mountain, which is a retro 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.

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.

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.