Infinite health
Get 179 barrels in challenge #17.

Infinite turbo
Get 8 zappers in challenge #4.

Unlock All Cars
Get 11 bonus stunt items in challenge #8.

Get All Items
Get 30 barrels in challenge #7.

Get all worlds
There is a hidden key you can use in challenge #18 to unlock all of the worlds in the game.

Infinite Ammo
Get 50 barrels in challenge #18.

Timer speed
Intentionally hit 13 Detour Signs while completing Challenge 15.

Gadgets for completing challenges

Challenge 1: Laser Cannon
Challenge 3: Sonic Boom
Challenge 4: Atom Blaster
Challenge 7: Freon Bomb
Challenge 9: Energy Shield
Challenge 10: Jet Booster
Challenge 13: Super Zapper
Challenge 15: Magnet Mine
Challenge 16: Doom Disks

Underworld Track
Successfully complete Challenge 2.

Glacier Track
Successfully complete Challenge 11.

Sewer Pipe Arena
Successfully complete Challenge 5.

Crankshaft Docks
Successfully complete Challenge 8.

Treadwell Plaza
Successfully complete Challenge 14.

Underworld Arena
Successfully complete Challenge 17.

Sho-Stopper vehicle
Successfully complete Challenge 6.

Surf Crate vehicle
Successfully complete Challenge 12.

Krazy 8s vehicle
Successfully complete Challenge 18.

HW Prototype vehicle
Successfully complete all missions in adventure mode.