Venus is the Trinity's goddess of space. She is merged with the otherworldly parasite Abaddon. Her appearance is deceiving as her full form is beyond the threshold of human comprehension. What you see is only but a sliver of her true form that has been able to slip into our reality. Why Venus has come to our plane of existence is simply out of boredom while waiting for Mother's (the head of the Trinity) plan to unfold. This action goes against Mother's plan, but perhaps that's part of the plan after all?
Venus appears along with her sister Aeon in Double's story mode.
Venus was revealed to be a potential DLC character among 31 other characters during the Skullgirls Indiegogo fund raising campaign. She was an early fan favorite, and had made it through the first round of voting, but simple sex appeal proved to be not enough amongst the Skullgirls community, and she was eliminated in the second voting round.
Venus' speculated play-style is best left in the words of Lab Zero games themselves:
"The lady is only the central part of a much larger creature. If the rest of her is visible, the observer has already been engulfed. There is no safe place when fighting her as the very fabric of the universe unravels into mouths, claws, and locusts devouring her prey’s flesh from every angle."
"Venus’s own body tantalizingly distorts to reveal monstrous elements. Body parts bloom from seemingly nowhere, sometimes releasing swarms of locusts to assault opponents from every angle. She can open holes in space, move and teleport in unexpected ways, or even distort the playfield itself. Even her own attacks may be displaced and modified."Lab Zero Games
How this could all work is still to be seen. Indeed, Venus will have to be selected by fans as one of two new DLC characters long before we will know anything beyond simply speculation and fantastical stories.