Dark Dynasty is the 21st episode of Season 10. It aired on May 6th, 2015.
Summary
THE WINCHESTERS MEET THE STYNES — Dean (Jensen Ackles) and Sam (Jared Padalecki) investigate a bizarre murder and realize the killer bears the same tattoo as those from the Styne family. Eldon Styne (guest star David Hoflin) attacks Dean and a brutal fight ensues. Meanwhile, Castiel (Misha Collins) acts as referee when Charlie (guest star Felicia Day) and Rowena (guest star Ruth Connell) are forced to work together on the Book of the Damned. Crowley (Mark Sheppard) discovers his mother is missing and knows she’s up to something so he turns to an old enemy for help. Robert Singer directed this episode written by Eugenie Ross-Leming & Brad Buckner (#1021). Original airdate 5/6/2015.