Nice find! My hopes for classic costumes have been renewed! :)

Very nice! I was just telling my friend the other day how there should totally be a classic Cyborg skin.

My bet is that there are a lot of things hidden away in different game modes. I think each character may have at least 3 costumes unlocked directly from the game. The 2nd alt is unlocked through the Archives, and another one is hidden in different game modes.

So far:
Boss Grundy - Bead Classic Battle with any character
Yellow Lantern - Win a ranked match
Elsworld Flash - 3 star all STARlab missions
New 52 Nightwing - Reach level 30
New 52 Green Arrow - Beat The MAX Battle

With the exception of Grundy, these seem to be the obscure characters that didn't get any pre-order bonus skins.

I didnt know about new 52 green arrow!! So you gotta beat classic battles on max to unlock that?? Also new 52 shazam by besting his lab missions I heard rumors of a sinestro in his classic blue costume as well

No you have to play an unlockable mode called Max battle. Masically beat all charcaters while the game is preset on hardest difficulty.

Also anyone here owns the strategy guide of Injustice? I'm sure all the games unlockables should be listed in there

I have it, while I haven't looked through it thoroughly, it looks pretty barebones outside of the archives.

[edit]: I finally gave the guide more of a look over and it actually does list all the know costumes and how to unlock them. It's actually very small section.
I'm starting to have my doubts now about the New 52 Green Arrow as there is no mention in the guide for him, or anything else besides what is already know for unlockable skins: New 52 Flash, Boss Grundy, Yellow Lantern, Godfall Superman, Elseworld Flash and Kryptonite Lex are all mentioned in the guide and how to unlock them.

Damn, Elseworld Flash and New 52 Green Arrow are tough to get.

It is hard to believe that that they wouldn't have a classic Harley skin in the game. There are probably a bunch of skins that are being saved for future DLC, just to keep that cash cow mooing.

There's going to be so much. Which I don't mind. I won't buy them all but if there are ones I want, i'll get them.

Damn, I just got around to learning green arrow today...I want that skin!

Whenever I get around to learning Grundy, I will be exclusively using the Boss Grundy skin. So gangster.

Can't wait to see what skins come with the compatibility packs.