Ill start this off by openly admitting I dont have solid proof. If you made it past that line , throw that tinfoil hat on because it's about to get a little smokey in here! So many people have speculated that eris morn is "evil" i agree with that half heartedly. Seeing as how the lack of story and narrative in Destiny prevent drawing a specific line between good and evil with its lack of content and plot implementation (not bashing just truth). Back to the larger point. Ive been pouring over grimiore lore for the past couple weeks and theres something ive noted in the stories gameplay and the lore itself. An epiphany if you will. Eris' rock (not on caydes map) is speculated as her dead ghost or some other form of her lost light. My theory is that it is actually a legal binding agreement of commitment, serfdom, slavery, etc.. The contract you ask? Life for information on enemy movements. Tinfoil hats are on right, because heres where it gets bumpy. As we all now someway somehow eris survived that pit. I theorize that rock is what keeps her alive. I also believe its a makeshift communications device one that hasnt been active since the lead commander of the hive had fallen in his fortress. Eris said so herself. Secondly it only regained transmission on phobos when we see the Taken King for the first time. "Fingertips on the surface of my mind!" At that moment Eris' will is ripped from her and Oryx is in control for the remainder of the game. As the Books of Sorrow conclude at "L". Oryx realized that his life was truly in jeopardy and that if indeed his life is threatened, ya know killing his echoes multiple times throughout the story, kinda like horcruxes for you HP fans ;), and then finally raiding him. Oryx would need a way to break the contract with his worm and thereby attatching his soul to one last horcrux that was sustained in a containment field and that could never run out. Grimiore Card , Books Of Sorrow , L : Wormfood Break the bars, make a new path, eat the light (Paraphrasing) Enter the Community voted Most Lore Intensive Weapon in the Game! Touch of Malice. Oryx's final horcrux. Eris has the the gaurdian create living quarters for Oryx's soul. The soul feeds off the light of the Gaurdian wielding it feeding the soul of Oryx and draining the Travelers light in the process. The gaurdian has now become the last horcrux of Oryx. What could go wrong?