Nintendo made Slime's appearance in Mario Sports Mix totally official today by adding the character to the game's official site. Word of the character's appearance leaked out earlier in the week.

Slime is flagged as "Tricky" play style. For his Special Shot, he calls upon other Slimes to form a tower and get some extra height. Visit the official site for a video.

This is what the full roster looks like:

The site also has details on some additional stages:

Wario Factory

A court on a conveyer belt that's located in a secret factory. Watch out for items that come down the belt! Compatible with all four sports.

Junior Street

A rich "bonus court." When you shoot from atop the bonus panels, you'll get increased points. It's possible to get 10 times the points in some cases. Compatible with volleyball, basketball and hockey.

Koopa Castle

A dangerous court. Be careful of the bubbles that fly up from below the court. Compatible with all sports.

Waluigi Pinball

A pinball court that's operated by Waluigi Mecha. Watch out for the iron ball that rolls around. Compatible with volleyball, dodgeball and hockey.

Ghost Ship

A sea-based court on the deck of a ship. Break the boxes that are on the deck, and Dry Bones characters will come out. Compatible with all sports.

Table Western

A turntable court that's set on a rail line in a wastelands area. Trolleys that pass by will toss bananas and coins at you. Compatible with all sports.

Starship

A sky-based court on the deck of an air ship. Pick up crystals for a chance at a bonus up. Compatible with all sports.