Enter The Dominatrix started out as DLC for Saints Row: The Third, then got turned into the full blown sequel we now know as Saints Row IV. If you are interested in seeing how the DLC was going to turn out, then you can buy Enter The Dominatrix, which is now available to purchase as DLC for Saints Row IV.
Enter The Dominatrix plays like a behind the scenes documentary from a DVD with interviews from the characters in game. Enter The Dominatrix will also feature returning characters such as Zimos, Donnie and brings along new missions and badass weapons as well.
Enter The Dominatrix is now available for $6.99 or free if you bought the seasons pass.