‘They came to us’
Nintendo is constantly creating new concepts within their own wheelhouse, but they’re generally not known for stepping outside their comfort zone and interacting with other studios (even projects like Smash Bros. are generally limited to interactions with other Japanese publishers).
It makes sense then that Mojang and 4J (the developer that handles Minecraft ports) approached Nintendo for the new Minecraft Mario Mash-Up pack. Speaking to The Verge, Nintendo’s senior manager of licensing Damon Baker stated: “They actually came to us with what their vision was, and the extent of it, and blew us away. It still went through an official approval process through our art department at our head office in Japan, but it was really driven by them as the creative studios behind it.”
Since the connection was already there with the porting of Minecraft to Wii U, I doubt executives had a compelling reason to say “no,” and thus the DLC was born. I’m pretty surprised it’s a free update too, as even Microsoft charges money for the Halo pack on Xbox platforms. Hopefully we see more of this cooperation in the future — Nintendo will need to rely more on third-party support as the landscape continues to evolve.