When you have won the Ultimate Battle Tournament and defeated Marduk in the final battle go to the Park and challenge any of the following characters to unlock their Guardian Bakugan at the Bakugan Store. Before you can unlock it's evolved form you must first purchase the Guardian Bakugan and when you then defeat it for a second time their evolved form of their Guardian Bakugan will become unlocked.

Dan:
Pyrus Dragonoid evolved into Pyrus Delta Dragonoid II

Runo:
Haos Tigrerra evolved into Haos Blade Tigrerra

Choji:
Aquos Preyas evolved into Aquos Preyas II Angelo/Diablo

Julie:
Subterra Gorem evolved into Subterra Hammer Gorem

Shun:
Ventus Skyress evolved into Ventus Storm Skyress

Masquerade:
Darkus Hydranoid evolved into Darkus Blade Hydranoid

Marduk:
Darkus Vladitor evolved into Darkus Battle Axe Vladitor

At the start of a new game enter one of the following codes as your name to unlock the corresponding effect.

Unlock Bronze Warius:
Enter 44982493 as a code.

Unlock 1,000 BP:
Enter 33204429 as a code.

Unlock 5,000 BP:
Enter 42348294 as a code.

Unlock 10,000 BP:
Enter 46836478 as a code.

Unlock 100,000 BP:
Enter 18499753 as a code.

Unlock 500,000 BP:
Enter 26037947 as a code.