Fanatical key. Base game only.

Both the base game and the 2nd Encore upgrade are super cheap on Fanatical right now (only for another 2 days or so) so if you'd rather have the full package and wouldn't mind paying less than 2 bucks it's a fantastic deal on a great game:
https://www.fanatical.com/en/bundle/skullgirls-2nd-encore-complete-pack

Good luck, have fun