(Disclosure: This site contains product affiliate links. We may receive a commission if you make a purchase after clicking on one of these links. Read our affiliate disclosure for more info.)
Steam has Skullgirls: Big Band DLC free for a limited time. Requires the base Skullgirls games.
You might be able to add the dlc to your account even though you don’t own the game yet, if you plan on buying it in the future.