I've heard everything from 50 of those DAVLIN fusion rifles you obtain from different destinations to the daily heroic Promethean code mission with exclusive dialogue to even the exotic fusion rifle the pocket infinity. I believe that everyone of these things is a part of it. If u played the daily Promethean code mission and went to the door to enter the omnigoul mission it would let u scan the door. Cayde would say then u can't go there and that all the good stuff is " below " u with the emphasis on the below. Now if u look inside the room through the glass u can see 3 black pillars with yellow lines on them . These were added by bungie and will serve some sort of purpose in obtaining the sleeper stimulant. I think u will eventually have to charge them up using the pocket infinity of a complete DVALIN fusion rifle. This will require 3 people to do since there are 3 pillars. There have also been people who have glitched under the map and have been under Rasputin. Underneath is a secret room where I believe that u will receive the sleeper stimulant when u gain access to it. Lastly this past August game informer published a Taken King exclusive look in their magazine. In there was an article saying "However, in order to unlock the gun, players first have to collect relics of the Golden Age which have been scattered across the various locations of Destiny. After players bring these pieces back to Banshee-44 (the Tower's gunsmith), the ancient artifacts trigger a memory in the ancient Exo gunsmith, and he will invite players on an odyssey to repair and reactivate one of the Taken King's most striking exotics. Bungie doesn't want to spoil the story content of this mission, but it did say that there will be unique tasks and objectives required for completion, which might even include puzzles that are too hard for any one player to figure out on their own." So the DVALIN fusion rifles definitely play a big part in the quest for the sleeper. So thats all I've been able to come up with so far. Drop your ideas and comments below. PS: I also have a hunch that there are big hints in some of the physical collectors edition items like the poster, cards, and especially the treasure island book with caydes notes. So if u have the physical collectors edition be on the look out and ask questions.