Snowman Wario

Snowman Wario, also known as Snow Wario  , is one of Wario's many transformations in the Wario Land series of games. It is triggered by having a snowdrift fall on Wario's head. He is then covered in snow, reducing his walking speed (as well as disabling his ability to jump in Wario Land 4), but allowing him to defeat baddies when he touches them. Also, if he steps on a slope, he will turn into an uncontrollable rolling snowball able to break Snowman Blocks. When he hits a wall, he will become normal Wario. This transformation is functionally similar to Ball o' String Wario.

Wario Land 4

 * Nintendo 3DS Ambassador Program digital manual bio: "Press to move and  to jump. Press  on a slope to roll."