To unlock more rare cards, have a high CLvL
To get Dressing Room unlocked 1st Time, complete any offline story.
To unlock Billy Hatcher Video, use a keyboard and hold down the G + B letters at the title screen.
To unlock Cards, use a memory card with a save game from the following games:
Billy Hatcher And The Giant Egg Clippen card
Phantasy Star Online: Episode 1 And 2 Nano Dragon + Card
Sonic Adventure 2 Battle Rage Card
Sonic Heroes Beat, Hallo Rappy and Sonic Knuckle cards
Sonic Mega Collection Madam Umbrella Card
Sonic Adventure DX Sange Card