Play as Bebe:
Lose the Cowdays race without getting any health power-ups.

Play as Cartman Cop:
Hit Chicken Lover about five times with the salty balls in the Read A Book Day race.

Play as Damian:
Place 1st. on the New Year's race and be the only racer to touch the Millennium key.

Play as Death:
Win the Halloween race after only dropping off four candies at a time.

Play as Grandpa:
Win the Halloween race.

Play as Ike:
In the Memorial Day race, grab the hidden power-up on top of the airplane.

With any character, grab a Phillip Phart (Visitor or Jesus are good to use because their cars float). Use the Terrence Turbo on the right side, during the earthquake. Try to go as fast as you can to get a good height. Use the Philip Phart in mid-air. If done correctly, you will land on the airplane wing.
*Note: Be prepared to try this over and over...

Play as Jesus:
Place 1st in the Christmas race.

Play as Marvin:
Place 1st. in the Thanksgiving race without collecting any turkeys.

Play as Mephisto:
Place 1st. in the Independence Day race.

Play as Mr. Garrison:
On the Rally Days 2 race, activate all four checkpoints.

Play as Mr. Mackey:
Place 1st in the Spring Cleaning race.

Play as Ned:
In the Independence Day race, Collect over 12 Turbo Pick Ups (caffeine, Terrence, Philip, etc.).

Play as Pip:
Only activate checkpoints 1 and 4 on the Rally Days 2 race.

Play as Satan:
Place 1st. in the New Year's race.

Play as Scuzzlebutt:
Find a Phillip Phart on the Easter Egg Hunt race. Then find the waterfall and Phart your way to the Golden Cow next to the waterfall.

Play as Sheila Broflovski:
In the Easter Egg Hunt race, collect the Pot Pie next to the building.

Play as Shelly:
Place 1st. in the Valentine's Day race.

Play as Terrance and Phillip:
In the Christmas race, collect the 4 hidden power-ups.

Play as Tweak:
In the Spring Cleaning race, Collect 5 Caffeine pick-ups.

Play as Visitor:
Collect the hidden power-ups above checkpoint 1, and between checkpoint 4 and the wooden bridge in the Memorial Day race.