TMNT Mutant Melee (GC)

Casey Jones
Complete level 5 Subway.

Hun
Beat Mickey's story mode (bottom path).

Ninja
Complete adventure mode with Raphael.

Shredder
Complete adventure mode with Don.

Splinter
Complete adventure mode with Leo.

Unlock April
Complete the Ghetto (stage 6 top path).

Unlock Bamboo Level
Defeat Splinter's 6th Mission Lakeside Terrace (Bottom Path).

Unlock Sewer
Defeat Leo's 5th Mission (Sewer).

Unlock Subway
Defeat Leo's 3rd Mission (Turtles' Lair).