From the Super Mario Wiki
They ride ski lifts in World 5 and stand completely still unless they drop off on a slope. Yoshi cannot eat them, but he can step on their heads to rack up a few coins and defeat them. They're harmless to touch, but they do hog up the ski lift platforms, which can become a bit of a nuisance as they are solid and can therefore push the Yoshis around. A certain Dr. Freezegood appeared in Tetris Attack, allied with Bumpty.
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