If a screenshot from the Japanese Super Mario Galaxy 2 website is to be believed, Nintendo’s highly anticipated sequel will include two-player multiplayer.
The screenshot clearly indicates that while one player controls Mario using the Wiimote and nunchuk, a second player, using only a Wiimote, can control a Luma, a star-type creature introduced in Super Mario Galaxy.
The specifics of the actual gameplay are still unknown, but it appears that it could end up being similar to the co-star mode in the first game, albeit now with an actual second character on screen. According to Nintendo Everything, the Luma’s name is Baby Chico, and apparently, it’s able to take out enemies with a spin attack. Neither of these details have been confirmed, so keep that in mind.
Source: Nintendo Everything