How to give away Skullgirls + All DLC?

Since there's no pack or collection on Steam that contains the base game + those DLC, you won't be able to create one giveaway for it ...
You can either split it up or just send the DLC keys to the winner of the base game via email or steam (or drop them in a thread or on the GA itself). :X

i gave it away awhile ago and just listed it as the base game but indicated it had the DLC

Maybe create a ticket. Or wait for pro answer.

I'd just create a giveaway for the base game, then mention in the description that winner gets all DLC too.

there is a pack, but it's marked as dev-only. last changed 3 months ago, dunno if it was removed from the store or something else.

you will do better by creating giveaways for the base game.

I follow the path that was mentioned: just create a GA for base game, and if the DLCs are separate keys, I send them to the winner in email after they marked the gift received.

You can also make an "event" and create a whitelist for the DLCs. So you know that the people who entered has the game and is interested in playing / add the DLCs

You should have made the giveaway invite only if you wanted it to be only for those who opened this thread :P