- Miyamoto was pretty lenient with what Next Level did with Luigi, but there were certain directions that Miyamoto tried to steer Next Leve away from
- Miyamoto told Next Level, "Make something better today than you made yesterday."
- Miyamoto visited Next Level's studios twice
- the control scheme was changed 10 times
- multiplayer was a desired feature from the start
- the idea of multiplayer was intended for the original Luigi's Mansion, but didn't make the cut
- the idea of multiplayer revival was added into Dark Moon once Next Level saw the feature in Nintendo Land's mini-game

I'd like to say one last thing. We released Luigi's Mansion 12 years ago, and lots of people around the world said, "Make another one!" and "Let's make another one together!" Thanks to them, we're finally able to bring a new Luigi's Mansion to the world. What's more, this is "The Year of Luigi," with celebrations and everything, so on Luigi's behalf, I'd like to express my appreciation. - Shigeru Miyamoto
Link