These are the extra characters you can play as in Battle Mode

Hige Bandit 2:
Collect all 3 Red Hige Hige cards

Hige Bandit 3:
Collect all 3 Blue Hige Hige cards

Hige Bandit 4:
Collect all 3 Green Hige Hige cards

Mighty:
Collect all 5 Jetters cards

Mujoe:
Collect all 3 Yellow Hige Hige cards