Here you can use the Black Eye Orb to invade Leonhard and kill him. By this process you will get the Silver Mask, Crescent Moon Sword and Rosaria's Soul immediately. Now travel to the "Aldrich, Devourer of Gods" bonfire and use the elevator to go up to Gwynevere's bed chamber. At this point, Rosaria will be dead and you can loot the Black Eye Orb from her corpse. Then use a Homeward Bone or Coiled Sword Fragment to return to the last bonfire rested at (Bringing you to same place). Leonhard will then appear at the entrance and you must talk to him and exhaust his dialogue. Once he tells you to join Rosaria's Fingers, go to Rosaria's Bed Chamber and offer Rosaria a Pale Tongue.
(Note: Pale Tongue must still be in the inventory at this encounter, if you use it, he will not appear)