Same as Breath of the Wild and Mario Kart 8 Deluxe.
It sounds like Super Mario Odyssey‘s sales have hit a major milestone, a little over a month after it first launched. Speaking in an interview following the news that the Switch has hit 10 million units sold globally, Nintendo of America President Reggie Fils-Aim discussed the strong showing the Switch is having on the software front- highlighting The Legend of Zelda: Breath of the Wild, Mario Kart 8 Deluxe, and Super Mario Odyssey are all games that have achieved a higher than 50% attach ratio with the Switch.
This means that more than half of all Switch owners own a copy of those games. Meanwhile, Splatoon 2 has achieved a 25% attach ratio. It is unclear if Fils-Aime’s numbers are specifically for North America (which is the territory he oversees), or globally, though the former seems true, since otherwise Splatoon 2‘s sales would be implied to b 2.5 million- when it was already at over 3 million back in September.
Regardless, this is a stunning success by Nintendo- and yet again, it exhibits the importance that their own software has had in pushing the Switch to the levels of success it has experienced.