World 8-1 (New Super Mario Bros. Wii)
From the Super Mario Wiki
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This level is completely filled with lava. A dark volcanic ash cloud chases Mario from the start to the end of the level, slowly consuming the entire level. If Mario touches the cloud, he dies instantly. Volcanic debris also falls from the sky, and this is the first level with Lava Geysers. At some parts of the level, Mario finds a metal platform floating above the lava which begins to sink if Mario steps in it. Buzzy Beetles are very common in this level.