Pause the game and go to Extras menu. Then click the enter password menu.

Effect	Password
"Bat-Fight" Captions Red Brick	EWTPKA
"Festive Hats" Red Brick	PHHGPH
"Minikit Finder" Red Brick	JYJAFX
"Quest Finder" Red Brick	KNJBD8
"Studs Score Multiplier x 2" Red Brick	5MZ73E
AquaMan	V3GTHB
Atrocitus	ZGCEAJ
Bane	XZKLKQ
Batgirl	4LS32K
Batman (Zur-En-Arrh)	ZWQPJD
Beast Boy	YC3KZZ
Blue Beetle	APEKBV
Deathstroke	5SW59X
Doctor Fate	4HRERD
Frankenstein	FQ4ESE
Giganta	95U7BM
Kevin Smith	J6ANCT
Lobo	B5ABPQ
Music Meister	S7GSDE
Nightwing	N9CZ7S
Plastic Man	H2VB8Z
Red Hood	TRQTPS
Superboy	QDQ3YL
The Fierce Flame	NQ46RC
The Joker	9WTGLP