As with the proper Pokémon games such as Emerald, Dash has special stages that are unlockable only by going to events. There are 3 special courses and a combination of 4 others done in this manner. Below is a list & details of these courses:

The Four Deoxys

This combination of courses was given away at PokéPark's opening in March '05. It consisted of the 4 Deoxys forms, while they may have been accessible in the past, it was impossible to have all 4 collected into one cup

Munchlax

This course, given away at the World's Hobby Fair in Japan and at the Nintendo World opening in America, has you chasing along the Pokémon Munchlax, the pre-evolved form of Snorlax

Pikachu & Lapras

The way to get this course is as of yet unknown. It features you racing across Pikachu & Lapras

 
Flying Pikachu

The way to get this course is as of yet unknown. It features you racing across Pikachu with it's Balloons

 

 
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