Spine Coaster

Bonecoasters are rideable creatures made of bone used to aid Mario and company pass through the lava pits, toxic water pools, or reach far away places.

New Super Mario Bros. Wii
They first appear only in World 8-7 from New Super Mario Bros. Wii, a stage that can be unlocked by finding the secret exit in World 8-2. It also appears in multiplayer versus mode.

Bonecoasters are very useful throughout World 8-7 because they help Mario and his friends get the Star Coins in this stage and also prevent them from falling into the lava. However, the Bonecoasters often make risky maneuvers, passing through lava geysers and into the lava itself. Bonecoasters can stand the weight of Mario, Luigi, and both Toads on it. However, if all characters perform a simultaneous ground pound, it will fall. Also, Bonecoasters cannot hurt any character.

New Super Mario Bros. Mii
Bonecoasters have also appeared in the Wii U demo New Super Mario Bros. Mii shown at E3 2011. One is seen in a dark cavern that is filled with poison water, carrying Mario and friends once again.

Super Mario 3D Land
Bonecoasters later appear in Super Mario 3D Land. However, they only make the appearance in 2. Their design has changed into a three-dimensional figure. They also somewhat resemble Dry Bones.

New Super Mario Bros. 2
Bonecoasters once again appear in New Super Mario Bros. 2, though they act more like Skull Rafts from Super Mario World. Two Bonecoasters only appear in World 6-2, where they sail along the lava. Once a Bonecoaster has reached its stop, Mario or Luigi can ground pound its head to make it spit out a large amount of coins, or even a 1-Up Mushroom. A little detail was added in this game where the eyes glowed every time a vocal riff was heard. The third DLC group for Coin Rush implies that the second Course Pack will involve a Bonecoaster as a necessary part of the Course Pack.

New Super Mario Bros. U
In New Super Mario Bros. U, Bonecoasters weren't confirmed to appear in levels, but one appears in the world map instead. Mario and his friends can ride it to travel through the map to Rock-Candy Mines and Meringue Clouds.

Trivia

 * "Bonecoaster" is a combination of the words "bone" and "roller-coaster".
 * The Bonecoaster somewhat resembles a Bone Dragon, but its head is smaller in size, and there are no spikes on its back.
 * Whenever the Bonecoaster goes fast, especially on a slope, it lets out a dinosaur-like roar. A single Bonecoaster may let out multiple roars during a ride. The Bonecoasters in Super Mario 3D Land make a different noise.