@GameXplain Not sure if you guys noticed this but there appears to be a black glossy panel or button on the bottom of the right joycon. pic.twitter.com/fAGAnT9EIv

— Chris ╰('ω') ╯ (@_chrisro) October 22, 2016

Spotted on Twitter by user @_chrisro, the Joy-Con appears to have a button on the side of the controller when pulled out of the Switch Dock. My guess is that this is used for gameplay for multiplayer, as this side button could function as a trigger button of sorts.

Source: Nintendo Everything