Mario Kart: Double Dash Cheats

To Unlock...	You have to...
King Boo, Petey Piranha	Beat the Star Cup in Mirror Mode
Toad, Toadette	Beat the Special Cup in 100CC
All Cup Tour	Beat the Special Cup in 150CC
Tilt-A-Kart, Battle Arena	Beat the Flower Cup in Mirror Mode
Luigi's Mansion, Battle Arena	Beat the Mushroom Cup in 150CC
Mirror Mode	Beat the All Cup Tour in 150CC
Special Cup	Beat the Star Cup in 100CC
Alternative "Thanks" Screen	Beat the All Cup Tour in Mirror Mode
Alternative Start Screen	Beat the All Cup Tour in Mirror Mode
Luigi's Green Fire	Beat the Mushroom Cup in 50CC
Petey Piranha's Piranha Pipes	Beat the Star Cup in Mirror Mode
Toad's Toad Kart	Beat the Special Cup in 100CC
Toadette's Toadette Kart	Beat the Mushroom Cup in Mirror Mode
Birdo's Turbo Birdo	Beat the Flower Cup in 150CC
Waluigi's Waluigi Racer	Beat the Flower Cup in 100CC
Diddy Kong's Barrel Train	Beat the Star Cup in 150CC
Daisy's Bloom Coach	Beat the Flower Cup in 50CC
King Boo's Boo Pipes	Beat the Special Cup in Mirror Mode
Bowser Jr.'s Bullet Blaster	Beat the Special Cup in 50CC
Baby Luigi's Rattle Buggy	Beat the Mushroom Cup in 100CC
Koopa Paratroopa's Para Wing	Beat the Star Cup in 50CC
Toadsworth's Parade Kart	Beat the All Cup Tour in Mirror Mode

Steal items from other players:
In 2/4 player co-operative the person sitting on the back of a kart can steal items from other racers. The driver simply has to get up close next to somebody, (make both karts side by side) then the partner controling the items at that point in time can press the R/L triggers, depending on which side the opposing kart is, then you will end up with the other karts item. (if the other kart has no item obviously you can't steal anything from them)
(supplied by: Andy.H)

Head Start:
Right when it says GO at the start of a race you press A for a headstart.
(supplied by: retard)

Special Items:
To get certain items, you have to have certain characters. Below is the list of characters, what they give you, and what it does.

Mario:
Red Fire - Throws scattered balls of red fire ahead of you.

Luigi:
Green Fire - Throws scattered balls of green fire ahead of you.

Peach:
Princess Love Hearts - Allows you to run into and item on the ground(banana,green turtle shell,etc.) or someone else and knock them over.

Daisy:
Princess Love Hearts - Allows you to run into and item on the ground(banana,green turtle shell,etc.) or someone else and knock them over.

Yoshi:
Green Eggs - Rolls a green egg at the person in front of you and breaks open to give you a banana, green turtle shell, and a speed - up.

Birdo:
Pink Eggs - Rolls a pink egg at the person in front of you and breaks open to give you a banana and two speed - ups.

Baby Mario:
Dog on a Chain - Pulls you around the course knocking anything in its path over.

Baby Luigi:
Dog on a Chain - Pulls you around the course knocking anything in its path over.

Toad:
Golden Mushroom - Gives you one golden mushroom that called for lets you speed - up three times.

Toadette:
Golden Mushroom - Gives you one golden mushroom that called for lets you speed - up three times.

Koopa:
Red or Green Shells - Fire red shells to hit an opponent ahead of you. Fire green straight ahead to bounce and have a chance of knocking an opponent over.

Paratroopa:
Red or Green Shells - Fire red shells to hit an opponent ahead of you. Fire green straight ahead to bounce and have a chance of knocking an opponent over.

Donkey Kong:
Big Bananas - Drops a big banana that when hit breaks into three small bananas.

Diddy Kong:
Big Bananas - Drops a big banana that when hit breaks into three small bananas.

Bowser:
Big Bowser Shell - Fires a big shell similar to the green turtle shell.

Bowser Jr.:
Big Bowser Shell - Fires a big shell similar to the green turtle shell.

Wario:
Bombs - Throws a bomb that blows up when something hits it or when an opponent gets to close to it withen a certain amount of time.

Walugi:
Bombs - Throws a bomb that blows up when something hits it or when an opponent gets to close to it withen a certain amount of time.

Petey Piranha:
Randomly Picks One Out of All the Items.

King Boo:
Randomly Picks One Out of All the Items.
(supplied by: maverick102)