Raining Debris, from New Super Mario Bros., New Super Mario Bros. Wii, New Super Mario Bros. 2 New Super Mario Bros. U respectively.
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Raining Debris are molten rocks falling from the background. They only appear 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, not to mention hurting Mario or Luigi if they touch one. Mario and Luigi can, however, take refuge under the dark floating platforms as the debris will not penetrate this.
Raining Debris reappear in New Super Mario Bros. Wii, mostly found in World 8-1. In this game, they are much harder to dodge as Mario has to jump through a lava-filled land with mostly small platforms to jump on, drifting poisonous clouds, and rising lava spouts.
Raining Debris appear in New Super Mario Bros. 2, where they act just like they did in the predecessor. They are first found in World 6-1.
Raining Debris return to New Super Mario Bros. U. In this game, they resemble more of a Fireball but its function in this game is the same as in the prequels, only occur in Peach Castle, Meteor Moat and in the secret level Firefall Cliffs. Bowser's fireballs in The Final Battle are identical to Raining Debris. These obstacles also appear in the challenge Cloudy with a Chance of Fire.