As with any rework, Nunu & Willump are getting a fresh set of splash art and skin models to give them the visual upgrade they need.
Nunu himself has more defining features. You can see his hair and his childlike expression, unlike his old splash art that made him look more like a cretin boy who is definitely up to no good. Willump has moved more to a My Neighbor Totoro theme, looking huge, cute and fluffy.
As expected, his shared TPA and Zombie splash arts just got tweaks to his side.
Grungy Nunu & Willump also looks completely different from what it used to be. It was once a Sesame Street reference, with Willump looking like Cookie Monster and Nunu resembling Oscar the Grouch, but now it looks Monsters, Inc. inspired. Nunu is all warm and fuzzy in a monstrous pajama set, while Willump looks like a huge stuffed animal. (You can even see Renektoy in the corner!) The name of the skin will likely be changed as well, similar to Crimson Akali’s change to Infernal.
Nunu & Willump should be moving to live servers in patch 8.17.
Grungy Nunu & Willump
Nunu & Willump Bot
Demolisher Nunu & Willump
Sasquatch Nunu & Willump
Workshop Nunu & Willump
TPA Nunu & Willump
Zombie Nunu & Willump
This post will be updated when new information becomes available.