By beating the game, a player would get a secret password they could input at the main menu, which would unlock a special feature. For instance, the password "ARNOLD" would make all characters huge.
If you're playing as TT, TT still appears in the lobby of the homeworld.
From the other playable characters, both Banjo and Conker got their own games: Banjo in Banjo-Kazooie (1998) and Banjo-Tooie (2000), and Conker in Conker's Bad Fur Day (2001) and Conker: Live and Reloaded (2005). Diddy himself started as a sidekick in Donkey Kong Country (1994) for the SNES.
There are two endings to the game. One involves you driving the Wiz Pig off of the island. There is another ending if you go to his homeworld and battle him. In either event, both endings give you one of the secret passwords.
The two secret characters are Drumstick, a rooster, as well as TT, the clock that lives just outside the course doors.