Guys Deej said he can only show us the door/doorway, and Cozmo has Pocket Infinity equipped, why the hell would he have it equipped? Because the description for Pocket Infinity is "You cannot shake the feeling that this is less a weapon than a doorway"
Its the key! We need to do something with Pocket Infinity! I dont know what but something!
Edit: Its funny too cos i abandoned this idea a while ago and told my friends "all we have to do is wait for a specific mission to become the daily and it will give us that fusion core thing or the transmitter thing, bungie will decide when we get sleeper"
Then bam, new quest, it wasnt the daily but a new quest altogether
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I have a theory. After you blow open the doors with the grenade. Try exiting the door going back to the warmind entrance instead and try to get into the omnigul area room where those three yellow towers are. Then try to shoot those three towers as a team with the pocket infinity and see if the trap door in the floor opens.