Ok, so me and my bro both agree..Nunu needs a rework.
His idea, which I like, is this:
Nunu's Q,W, and E change based on who is active.
His new ult would be similar to Nidalee and Elise in this aspect: by activating his R, Nunu switches who attacks and uses abilities.
Starting out, Nunu is the active one. Activating his R would then switch it so that the Yeti is doing the attacks.