World 6 (Yoshi's Woolly World)
From the Super Mario Wiki
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World 6 is the sixth world of Yoshi's Woolly World. It is a mostly volcanic-themed world, featuring elements related to lava and ashy clouds. As in all other worlds, there are nine levels: eight compulsory, and one special level that is unlocked after all other Smiley Flowers in the previous levels in the world are collected.