Volcanic debris

Volcanic Debris is molten rocks first seen in Mario Party. They are often found falling from the background of volcano-based levels.

New Super Mario Bros.
Volcanic Debris reappears in World 8-8 of New Super Mario Bros., which is a level with many Kab-ombs. These rocks destroy blocks and set off the fuses on Kab-ombs, and hurt Mario or Luigi if they touch one. They can be defeated with a Super Star.

New Super Mario Bros. Wii
The rocks later appear in New Super Mario Bros. Wii, and is mostly found in World 8-1 alongside drifting poisonous clouds, Buzzy Beetles and rising lava spouts. Larger debris also appears, and can plow through several blocks before landing, in addition to taking up more space. Some Volcanic Debris also appears at the beginning of World 8-2.

New Super Mario Bros. 2
Volcanic Debris appears in New Super Mario Bros. 2, in which its role is the same as in its previous appearance. It's only found in World 6-1.

New Super Mario Bros. U/New Super Luigi U
In New Super Mario Bros. U and New Super Luigi U Volcanic Debris was replaced by Meteors and Bowser's Fireballs, though they have the same behavior.

Super Mario 3D World
Volcanic Debris also appears in Super Mario 3D World, with an appearance similar to Bowser's Fireballs in New Super Mario Bros. U. In addition to falling from above, it now creates a lava puddle upon landing. It only appears in The Great Tower of Bowser Land, being expelled by a volcano in the background, and in Hisstocrat Returns and Boss Blitz, in which it is generated by Queen Hisstocrat.

Mario Kart: Super Circuit
Volcanic Debris appears in Mario Kart: Super Circuit, where the volcanoes in the background of Lakeside Park launch it onto the track. The racers are burned if they run into it.

Mario Kart Wii
In Mario Kart Wii, Volcanic Debris appears on Grumble Volcano, where it is fired from volcanoes, and spins out racers that crash into it. It remains on the ground for some time after it lands.

Mario Kart 8
Volcanic Debris reappears in Mario Kart 8, where returns in Grumble Volcano. It moves slower than in Mario Kart Wii when it is falling to the ground.

Mario Party
Volcanic Debris first appears in Bowser's Magma Mountain in Mario Party, where it is launched from a volcano when a player lands on a Happening Space. They change the Blue Spaces into Red Spaces for two turns.

Paper Mario: Sticker Star
In Paper Mario: Sticker Star, Volcanic Debris is referred to as "meteors" and is only found in one level, Rugged Road. The rocks can still hurt Mario if he touches them, but now they can also harm him if he gets caught in the spot where the debris lands for about one second. In addition, the meteors also home in on Mario.

Paper Mario: Color Splash
Volcanic Debris appears in Paper Mario: Color Splash in the level Kiwano Temple. It appears at the end of the level, where it jumps out of the lava and hovers over the platform Mario and Huey are on. If Mario touches it, he will take 8 HP of damage.

Mario & Luigi: Dream Team
Volcanic Debris also appear in Mario & Luigi: Dream Team, where it is used as a weapon for Mount Pajamaja.

Captain Toad: Treasure Tracker
Volcanic Debris reappear in Captain Toad: Treasure Tracker. It rains down during the Draggadon and Gold Draggadon boss battles.