You probably don’t know DC villain Blackout a.k.a. Amunet Black, though chances are between Riddick, 24 and Battlestar Galactica, you almost definitely know Katee Sackhoff, so I guess it evens out.
According to EW, Sackhoff joins the fourth season of The Flash in episode 5, an Arrow crossover featuring Emily Bett Rickards' Felicity Smoak titled "Girls Night Out." She'll show up more than once, though this is how her initial appearance is described:
Blacksmith, a steely and badass boss of an underground black market for supervillains. Amunet uses every means possible, including the long list of metahumans under her thumb, to ensure her illicit enterprise thrives.
Sounds fun, and it'll probably get even more fun as things progress since Blacksmith ends up a kooky blend of organic and inorganic materials and lookin' a bit like a member of The Blue Man Group wandered in to a March of the Juggalos:
The Flash returns October 10th on The CW.