Super Mario games are the definition of family-friendly fare. Well, for the most part. I still can't get over Mario's drowning animation in Super Mario 64. He floats. You actually see his lifeless body, and it floats, Georgie.
Other than watching Mario's lungs fill with brackish water, you can count on Mario games to be colorful and imaginative romps that command an easy "E for Everyone" rating from the ESRB. But it looks like Mario is going to walk an ever-so-slightly shadowed path in Super Mario Odyssey, which has an "E10+" rating.
You won't find Mario Odyssey's rating up on the official ESRB site yet, but you can spot it on Nintendo's page for the game. The title is marked for "Cartoon Violence" and "Comic Mischief." By contrast, Super Mario 3D World for the Wii U is rated E and is marked for "Mild Cartoon Violence."
I've already made jokes galore about the seemingly dark content in Super Mario Odyssey, e.g. Mayor Pauline ruling over New Donk City with an iron fist in a velvet glove. That's all just silliness, though; I couldn't even begin to tell you why Mario Odyssey is rated E10+, or why it's marked for "Comic Mischief" when other Mario games aren't.
According to the ESRB's explanation of its ratings, a game is flagged for Comic Mischief when it contains "depictions or dialogue involving slapstick or suggestive humor." So I guess someone's either getting a pie in the face, cracking a boob joke, or getting a pie in the face while cracking a boob joke.
In all seriousness, Mario Odyssey's odd juxtaposition of realistic locales and typical cartoony Mario graphics must be responsible for the increased rating, at least in part. The slight rating uptick doesn't matter to anyone except maybe that one super-sheltered kid at the back of the class who's not allowed to play any game that's not rated E.
We'll uncover the whole truth when Mario Odyssey comes to the Nintendo Switch on October 27, 2017.