You can unlock various content, including additional modes, by satisfying the corresponding requirements indicated below.

Unlockable	How to unlock
16 Angels	Place 3rd or better in the Bowling Alley Tournament (Turbo mode)
Battle Spec	Place 2nd or better in the Attic Tournament (Nitro mode)
Bone Shaker	Place 2nd or better in the Mini Golf Tournament (Nitro mode)
Da Kar	Place 1st and complete goals 1 and 2 in all events (Nitro mode)
Dieselboy	Place 1st in the Mini Golf Tournament (Inferno mode)
Drift King 24/Seven	Place 3rd or better in the Bedroom Tournament (Turbo mode)
Hollowback	Place 1st in the Bedroom Tournament (Inferno mode)
Inferno Mode	Acquire 420 flames throughout the game
Muscle Tone	Place 2nd or better in the Bedroom Tournament (Nitro mode)
Nitro Door Slammer	Place 2nd or higher in the Bowling Alley Tournament (Nitro mode)
Nitro Mode	Acquire 146 flames throughout the game
Phantom Racer	Place 3rd or better in the Attic Tournament (Turbo mode)
Power Bomb	Place 1st in the Bowling Alley Tournament (Inferno mode)
Speed Bump	Place 1st and complete goals 1 and 2 in all events (Inferno mode)
Spine Buster	Place 1st in the Attic Tournament (Inferno mode)
Super Tsunami	Place 1st and complete goals 1 and 2 in all events (Turbo mode)
The Demon	Place 3rd or better in the Mini Golf Tournament (Turbo mode)