Super Smash Bros 4 and Ultimate developed by Bandai Namco.
This, hands down. Smash developed by Bandai Namco, best Nintendo-third party collaboration.
I mean... in other times i would say Pokemon developed by Game freak, but as a big pokemon fan... i have to say that Sword and shield are a big let down, big like gigantic.
Prediction: In 5 years Nintendo will Lauch a "Core Mario game" very similar to Astro Bot. That said, many will Ignore Astro Bot existence and say Nintendo created this concept.