I was playing Batman: Return to Arkham/ Arkham City and completed the story on February...

You only have one costume unless it was a bonus from preordering from the following:

Batman Beyond -- Pre-order Batman: Arkham City from GameStop.co.uk or MightyApe

Dark Knight Returns -- Purchase the Batman: Arkham City Collector's Edition, Any Store

Earth One Batman -- Purchase Batman: Arkham City from MightyApe

1970's Batman -- Pre-order Batman: Arkham City from ShopTo.net (UK) or Toys R Us (USA)

The Animated Series Batman -- Purchase Batman: Arkham City from MightyApe

I'd go for Batman: Arkham City. I played Batman: Arkham Asylum for the first time in a while yesterday and it's still awesome, got me pumped for Arkham City.

Batman: Arkham Asylum - haven't finished it yet (must get round to it) but the story is top notch.

Heard the same about Arkham City as well but 've not played it yet.

Batman Arkham City was better than Arkham Asylum in practically every way a video game could outdue its predacessor.
Batman Arkham City is the best Batman video game ever created IMO.

Hi,

The Arkham Bundle contains the Nightwing Bundle Pack, Robin Bundle Pack and Arkham City Skins Pack.

Nightwing Bundle Pack:

Nightwing character is playable in all challenge maps in the game, as well as two additional challenge maps that are included with the pack: Wayne Manor and Main Hall. The pack also contains a bonus Animated Nightwing character skin.

Robin Bundle Pack:

Robin character is playable in all challenge maps in the game, as well as two additional challenge maps that are included with the pack: Black Mask and Freight Train. The Freight Train Escape challenge map is a unique take on Arkham City, featuring
brawler gameplay on a 2D plane. The pack also contains two bonus character skins: Red Robin and Animated Robin.

Arkham City Skins Pack:

The Arkham City Skins Pack contains seven bonus Batman skins: 1970s Batman, Year One Batman, The Dark Knight Returns, Earth One, Batman Beyond, Animated Batman and Sinestro Corps Batman. The 7 Batman skins can be used in all challenge maps immediately
and in storyline mode upon completion of main story.

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Based on the information given in the descriptions of these individual DLC's it seems that these are DLC characters available in challenge maps. The only one that is available as far as skins in the main story line are the Arkham City Skins Pack.