World 5 (Yoshi's Woolly World)
From the Super Mario Wiki
World 5 is the fifth world of Yoshi's Woolly World. It is a mostly ice-themed world, featuring elements related to snowballs and ice blocks. 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. Completion of this world unlocks World 6.