[Skin Concept] (With Photoshop)

His ult is a big surprise party like Fiddlesticks', with confetti and stuff,

and Willump could be a giant Piñata. Thus the 'Confetti Yeti'

and blood boil could be Nunu blowing a kazoo to invigorate an ally

Waaaaay too much going on the pic, but pinata willump would be funny