** DISCLAIMER
The key is from a bundle that I purchased about a decade ago. The base game, Gotham CIty Imposters, has been removed from Steam and it is not playable anymore. So I am unsure if the key can be activated on Steam, nor it actually gives you something when it is activated. I have no responsibility even if it does not work properly. I am giving it away just hoping there might be someone who can find a good use for it.
Yes, I failed to find a place to throw it away.