The following comes from a Reggie Fils-Aime interview featured in Unlocked: The World of Games, Revealed.
On using an existing IP for an idea or creating a new one
“We think about what’s going to be fun, new gameplay. And as we identify that gameplay, we then think about which IP does it fit best? Maybe it needs to be a new IP. But it’s this constant iteration of, what’s the gameplay innovation, and then how do we bring it to life That’s the Nintendo ways of doing things. It’s not right for everybody, but certainly it’s right for us.”
On the creation of Mario
“Mr. Miyamoto, Mr. Tezuka created this character with a mustache so that you could separate his nose from the rest of the face. A character that was given overalls so that you could tell the difference between his arms and his legs. I mean all of these little things that became iconic to who Mario is today, but again at the heart was a focus on craftsmanship and a focus on making every subsequent Mario game unique and compelling.”