How do I unlock characters!?

You unlock characters by beating Gem Cups on Adventure Mode.

To access a gem cup, get 4 CNK tokens of one colour. As you complete each cup, more characters will open for you:

Red Gem Cup = Dingodile
Blue Gem Cup = Polar
Green Gem Cup = Zem
Purple Gem Cup = Zam

Performing 50 boosts with the two different teams also unlocks two characters:

Team Bandicoot = Pura
Team Cortex = Fake Crash

There are four characters in each of the four teams (16 characters in all!). I have only unlocked four secret characters, but I have ways of finding out secrets!

Here' s a list of all the characters in the game and how to unlock them all (tip: characters with "default" next to them are available without unlocking!)

Team Bandicoot (Blue cars):
Crash Bandicoot: Default
Coco Bandicoot: Default
Crunch Bandicoot: Default
Fake Crash: Do 50+ boosts on any track in adventure mode as Team Cortex

Team Cortex (Red cars):
Doctor Neo Cortex: Default
Doctor N. Gin: Default
Tiny Tiger: Default
Doctor Nefarious Tropy: Beat all of his records in time trial mode

Team Alien (Yellow cars):
Nitrus Oxide: Default
Zem: Get the purple gem
Zam: Get the blue gem
Real Velo: Beat all of his records in time trial mode (beat Tropy' s first!)

Team Animal (Green cars):
N. Trance: Default
Polar: Get the green gem
Dingodile: Get the red gem
Pura: Do 50+ boosts on any track in adventure mode as Team Bandicoot

Sorry! I was wrong about Velo! Here's the truthful list.

Team Bandicoot (Blue cars):
Crash Bandicoot: Default
Coco Bandicoot: Default
Crunch Bandicoot: Default
Fake Crash: Do 50+ boosts in any race in adventure mode as Team Cortex

Team Cortex (Red cars):
Doctor Neo Cortex: Default
Doctor N. Gin: Default
Tiny Tiger: Default
Doctor Nefarious Tropy: Beat all of his time trial mode records

Team Alien (Yellow cars):
Nitrus Oxide: Default
Zem: Get the Blue Gem
Zam: Get the Purple Gem
Real Velo: Complete adventure mode as both Team Bandicoot and Team Cortex.

Team Animal (Green Cars):
N. Trance: Default
Polar: Get the Green Gem
Dingodile: Get the Red Gem
Pura: Do 50+ boosts in any race in adventure mode as Team Bandicoot