Let me delete if this doesn't work, this may totally not work.

I'd rather only people enter that don't have any Orcs Must Die! 2 DLC that is included in the Complete pack "Are We There Yeti?", "Fire and Water Booster Pack", "Family Ties Booster Pack". Anyone that owns nothing or owns just the base game, feel free to enter.

Some additional info:
It's an old key from the Humble Bundle 2022 Handheld PC Power Bundle that may already be used. This is also the key for the product "Orcs Must Die! 2 - Complete DLC" from within the bundle so it implies it should just be the DLC but I'm unsure on that. When I tried to redeem the key just now on my account that already owns the base game and all the DLC, I received this link from the SteamDB extension - https://steamdb.info/sub/18485/ which is what the giveaway is for. So this may just be the base game + all the DLC or just the DLC. Enter at your own risk.