kaid
Smash Master
As those of us with a Wii can tell you, Legend of Zelda: Twilight Princess is quite literally the best Zelda game ever. And the single most important character in the game, short of Link himself, is Midna, an imp with magical powers from the Twilight Realm who is, at least at the beginning, using Link for her own ends.
The major gameplay mechanics that involve Midna has her either hiding in Link's shadow, or riding on his back when Link transforms into a wolf. Like Kazooie to Banjo, she is the source of most of "your" abilities while in this form, but by herself, she would not be as canon a character.
As a 4-legged character, Wolf Link adds a new style of play to Smash, and Midna gives him more moves than the monotonis basic attacks. Using her headdress as a massive hand, Midna covers about half the A moves for this character, and most of the B moves.