Pause screen select "Extras" and then select "Enter code".

Effect	Code
Aquaman	V3GTHB
Atrocitus	ZGCEAJ
Bane	XZKLKQ
Batgirl	4LS32K
Batman	ZWQPJD
Beast Boy	YC3KZZ
Blue Beetle	APEKBV
Deathstroke	5SW59X
Doctor Fate	4HRERD
Festive Hats	PHHGPH
Fight Captions	EWTPKA
Frankenstein	FQ4ESE
Giganta	95U7BM
Kevin Smith	J6ANCT
Lobo	B5ABPQ
Minikit Detector	JYJAFX
Music Meister	S7GSDE
Nightwing	N9CZ7S
Plastic Man	H2VB8Z
Quest Detector	KNJBD8
Red Hood	TRQTPS
Studs x2	5MZ73E
Superboy	QDQ3YL
The Fierce Flame	NQ46RC
The Joker	9WYGLP