Cappy

Cappy is a character featured in Super Mario Odyssey. He is Mario's main ally during the game, and helps in various ways.

Super Mario Run
Though Super Mario Odyssey is the first game which Cappy is physically present, his first appearance in a game is in Super Mario Run[1]. To promote Super Mario Odyssey's appearance at E3 2017[2], a statue of Cappy was made available as one of the objects in the Kingdom Builder on June 14, 2017, and it costs 2,000 coins. When it is tapped, it will change to its original ghost top hat form for a few seconds, while a voice can be heard exclaiming, "Cappy!" The description of this statue reads: "Straight from Super Mario Odyssey! This statue is of Mario's new partner Cappy."

Super Mario Odyssey
Cappy is Mario's partner in Super Mario Odyssey. Mario can throw Cappy in various ways; in a straight line, in a way that spirals around Mario, and in a boomerang-like shot. Cappy can help collect items (such as coins) for Mario, and also has the ability to damage enemies. When thrown at enemies or objects, Cappy seems to "possess" them, allowing Mario to control them to get across certain parts in stages. This ability is officially known as "capture." For example, when thrown at Bullet Bills, Cappy allows Mario to transform into them and fly above gaps in the ground. Cappy also informs the player of various aspects of the game and of the environment around them, such as the local coins that can only be used in that world.

Cappy's role in the main story is unknown for now, although it is assumed that he is Mario's sidekick. Cappy can also be controlled by player two when in co-op mode. Cappy's normal form is a white top hat with large eyes, with blue wisps of hair coming out the top of it. Under the hat is his body, which somewhat resembles an Eerie[3] When transformed into different hats, such as Mario's cap, Cappy's eyes will appear on that hat.

Reference​s
[1]. Super Mario Run

[2]. Nintendo E3 2017

[3]. Eeries