New Super Mario Bros. 2 offers three save files. But if you decide to share the game with someone else through one of these slots, keep in mind that it tracks the coin total across all saves.
So it’s like this: if you amass 500,000 coins in your slot and a family member nabs another 500,000, the overall coin total will come in at 1,000,000.
Some may see this is a bad thing since you can’t accomplish the one million coins goal on an individual save. On the other hand, gamers tend to keep/play handheld titles for themselves, so it won’t be much of an issue in most cases.