From the Super Mario Wiki
Conveyor Belts (or simply conveyors) are platforms found in many Mario games. They are able to carry the player from one place to another without them having to move at all, and can serve as an obstacle or a means to travel faster, depending on the direction the player is heading.
Mario vs. Donkey Kong series
Conveyor belts are frequent mechanisms used by Mario and Mini toys throughout the Mario vs. Donkey Kong series. Their design in these games generally features a row of arrows running along their body, pointing in the direction the belts on the conveyor belts move. They are always horizontal and run either left or right. Conveyor switches often accompany conveyor belts and allow the player to change the direction of all conveyor belts on-screen in order to solve puzzles conveniently. Conveyor belts are shown to be able to carry enemies, even fallen Thwomps, in their assigned direction.
Mario vs. Donkey Kong
In the first installment of the series, conveyor belts are first found in Level 1-4 of Mario Toy Company. Their color scheme depends on the world they appear in. Their main purpose is carrying Mario through tight passages while he crouches. Conveyor belts can also be used to ferry keys into more accessible areas near the exit. They also significantly impede Mario's walking speed if he runs against them, although he can still successfully walk in their opposite direction. This is the only game in the series where conveyor belts are semi-solid, meaning that they can be jumped on from underneath.
In levels with conveyor belts, Mario often comes across gray buttons that he can jump on and press to change their direction. Each button has two red light bulbs on its sides, alternating whenever the button is pressed to signal the change in direction.
Mario vs. Donkey Kong 2: March of the Minis
Conveyor belts continue to appear in Mario vs. Donkey Kong 2: March of the Minis, debuting with Room 1-7 of Mushroom Mayhem. From this game onward, they all appear as gray and are completely solid. Mini Marios that enter a conveyor belt are glid by the conveyor belt in direction it moves until reaching its end. Mini Marios turn around when they encounter a conveyor belt running in the opposite direction.
In many levels with conveyor belts, there are also green oblong switches with two arrows pointing away from each other. These are positioned in the walls and the player can tap them with the stylus to change the direction of all conveyor belts in a level simultaneously.
Mario vs. Donkey Kong: Minis March Again!
Conveyor belts and switches work the same in Mario vs. Donkey Kong: Minis March Again!, where they are introduced in Room 3-2 of Magnet Mania. Magnet Mania also features a tutorial level that showcases the conveyor belt.
Mario vs. Donkey Kong: Mini-Land Mayhem!
In Mario vs. Donkey Kong: Mini-Land Mayhem!, conveyor belts are considerably thinner than in the previous two appearances, though they function in the same way nonetheless. They are the main focus of Teatime Twirl, which also marks the debut of Purple Conveyors. Instead of being fixed in place, the latter can be drawn between any two purple rivets using pieces acquired in a level. Conveyor Switches affect the Purple Conveyors the same as generic conveyor belts. After Teatime Twirl, both the fixed and the purple variants continue to appear commonly throughout the game. At page 16 in the game's instruction booklet, normal conveyor belts are called Gray Conveyors to distinguish them from the purple variety. It is also expressly specified in the booklet that Gray Conveyors cannot be moved.
Mario vs. Donkey Kong: Tipping Stars
Super Mario series
Conveyor Belts appear in Super Mario Bros. 2, Super Mario Bros. 3, Super Mario World, Super Mario Land 2: 6 Golden Coins, Super Mario 64, New Super Mario Bros., Super Mario Galaxy, New Super Mario Bros. Wii, New Super Mario Bros. 2, and New Super Mario Bros. U. In Super Mario Bros. 2, they are only found in World 7-2, where their color is purple/red and enemies are not affected by it, unlike later games. In Super Mario 64, it makes its first 3D appearance with its color being yellow and having arrows showing the direction it is pointing in the direction it normally goes. In World Flower-Castle in New Super Mario Bros. 2, there are two Conveyor Belts that can change directions and colors (blue or red) by hitting a yellow switch, one of which appears in the battle against Lemmy.
Conveyor Belts can be used in Super Mario Maker and Super Mario Maker for Nintendo 3DS, where their speed can be adjusted by shaking them. Their direction and length can also be changed. Pressing a P Switch causes the Conveyors to stop moving. They also reappear in Super Mario Maker 2. In Super Mario Maker 2, Conveyor Belts can be placed diagonally, acting as slopes. Additionally, a new type of Conveyor Belt is introduced that is toggled by ON/OFF Switches, switching direction when one is activated.
Mario & Luigi: Bowser's Inside Story
Conveyor Belts appear again in Mario & Luigi: Bowser's Inside Story, where black-colored ones are found in Bowser Path. Bowser can be seen going against a conveyor belt when for part of his conversation to the Shy Guys he released from the cage.
Super Smash Bros. Brawl
Conveyor Belts also appear in Super Smash Bros. Brawl, as a Custom Stage Builder part. They are unlocked by creating at least five custom stages.
Yoshi's New Island
Conveyor Belts are present in Yoshi's New Island in the level Hotfoot Hurdle. They are rather short and floating above lava. They run left (as signified by the three green arrows displayed on them) to make it more difficult for Yoshi to advance to the right. Conveyor Belts are usually placed in rows or one above the other.
Yoshi's Woolly World / Poochy & Yoshi's Woolly World
Conveyor Belts appear in World 6-6: Feel Fuzzy, Get Clingy in Yoshi's Woolly World and Poochy & Yoshi's Woolly World, where they are made of the hooks from a hook and loop fastener (colloquially known as Velcro). Because of this, Yarn Yoshi can cling onto them as they move (hence the level name), allowing him to access unreachable areas. Burrberts are often found stuck to Conveyor Belts and carried by them.
Names in other languages