This is how to unlock the Protoganist Bakugan in the game. All the battles must be do in the park and after beating the game.

Unlockable	How to unlock
Cycloid	Join Julie In a Tag Team Battle.
Dragonoid	Beat Dan in a One on One Battle.
Fortress	Join Dan In a Tag Team Battle.
Gorem	Beat Julie in a One on One Battle.
Harpus	Join Shun In a Tag Team Battle.
Preyas	Beat Marucho in a One on One Battle.
Sirenoid	Join Marucho In a Tag Team Battle.
Skyress	Beat Shun in a One on One Battle.
Tentacler	Join Runo In a Tag Team Battle.
Tigrerra	Beat Runo in One on One Battle.