Planning on playing Mario Kart 8 Deluxe on-the-go with a friend? You might want to grab an extra Switch Pro controller.
Polygon has confirmed that Mario Kart 8 Deluxe doesn't support the JoyCon Grip in local wireless multiplayer modes. That means players can't combine two JoyCons into the comfortable JoyCon Grip when playing split-screen--even if one player uses the Switch Pro controller, the other player still has to use a single JoyCon. Why? Because every JoyCon counts as its own controller, so a JoyCon Grip counts as two controllers for one person, and Mario Kart 8 Deluxe apparently only supports a two controllers max for wireless split-screen play in Tabletop Mode.
Remember that the Nintendo Switch's two detachable JoyCon controllers are meant to be split up and used by two players while in Tabletop Mode, facilitating the popular arcade style play the system is known for. In fact, the official Switch reveal video shows people playing Mario Kart 8 Deluxe in wireless splitscreen using two individual JoyCons. Interestingly enough, Polygon doesn't answer the more pertinent question--is the JoyCon Grip supported in two-player splitscreen when the Switch is docked?--and I'm pretty sure this restriction is in place for a good reason.
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The Nintendo Switch downclocks its internal NVIDIA Tegra processor when both wireless modes--Tabletop Mode or Handheld Mode--are active, thus reducing power draw and heat. I would imagine the Switch lowers other specific features as well to preserve battery drain--possibly Bluetooth radio signals and the like. When the Switch is docked into is cradle, its supplied with a steady source of power and the Tegra chip fully unlocks its GPU performance to hit the targeted resolution and frame rates of any given game or software.
If Mario Kart 8 Deluxe doesn't have the same single JoyCon restriction while docked, then it stands to reason certain features could be downgraded alongside the system's GPU.
As we all know, Nintendo's FAQ says up to eight JoyCons or Switch Pro Controllers can be paired to a single Switch console at a time. However, this is likely only for docked mode, not Tabletop modes. Nintendo also confirms that those eight controllers have to be Switch Pro controllers.
Nintendo explains the situation here:
The Nintendo Switch Pro Controller is always counted as 1 controller. Example: Eight people can play, each using a Pro Controller.Up to eight wireless controllers can be connected to the console. However, the maximum number of controllers that can be connected will vary depending on the type of controllers and features that are used. For example:
The right and left Joy-Con each connect as individual controllers to the console, so if you connect both of them wirelessly then it counts as 2 controllers.
Example: Four people can play, each person using one left Joy-Con and one right Joy-Con controller.
Even if the Joy-Con controllers are attached to the Joy-Con grip, it counts as 2 controllers that are connected.
Example: Four people can play, each using the Joy-Con controllers attached to the Joy-Con grip.
When the Joy-Con controllers are attached to the console, they do not count against the number of controllers that can be connected.
The Nintendo Switch Pro Controller is always counted as 1 controller.
Example: Eight people can play, each using a Pro Controller.
Important: On top of the limit of connected controllers by type, the number of connected controllers is also determined by the features being used on the controllers, and whether local communication is being used.