Requires the base game Skullgirls.
The DLC is basically another playable character/fighter.
From the Steam page:
"Beowulf enters the ring!
Loosely based on the epic poem of the same name, Beowulf is a wrestler returning after a long hiatus. Literally armed with Grendel's severed arm and his folding chair, The Hurting, Beowulf fights to restore his faded glory.
Thanks to the incredible support of Skullgirls’ fans, Beowulf is the fourth of five additional characters funded by Lab Zero’s Indiegogo campaign to be added to Skullgirls Encore. Beowulf features a repertoire of over-the-top wrestling moves, a unique crowd hype gameplay mechanic, and the same stunning, feature-quality animation and great gameplay you've come to expect from Skullgirls and Lab Zero Games!"
As far as I'm aware, he's been free since his release because Skullgirls makes every new character free for a set period after release.
Good reminder for those who have the game though.