Which DLC is this? Am I able to give it away?

https://www.steamgifts.com/discussion/ONZG6/indiegala-golden-flash-giveaways-shame-of-the-dead-part-3#RcOzo0k I've never used this method to check a dlc, but i would imagine it'd work for that, as long as you either already own the dlc, or don't own the base game. If you do own the base game, and not the dlc, then of course it will activate it for your account. Or you can wait and someone that knows the answer for that specific key from hb will hopefully come along and help you.

This is the DLC listing on SG for the Batman Arkham Origins DLC that was added to the Humble WB Games Bundle..

Batman: Arkham Origins - New Millennium Skins Pack

Link to the Steam Store - Batman Arkham Origins New Millennium Skins Pack

If you make a giveaway for this you will want to add the winner to steam and look if they have this. As mentioned on the Steam store it can be obtained by purchasing the Season Pass for the game as well as a single purchase.

I own all of the DLCs listed on steam, so if you want me to test the key to check, feel free to add me. but it's probably what Fate said.

Thanks Fate & everyone.