BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
In Dark Lord of the Sith 25, Vader uses the Mask of Lord Momin to open a gateway through the Force. In the gateway, Vader confronts his past through a series of visions, meeting important people from his past, including Anakin's mother, Ahsoka, and Padme.
FORTRESS VADER: FINALE! The FORTRESS is complete. The door will be opened. VADER finds everything he has ever desired. THE DARK LORD gets everything he deserves.