Moelach is an ancient spren, likely one of the Unmade, considered evil by Taravangian, and appears to be responsible for the Death Rattles uttered by some people when they die. These utterances have, thus far, offered Taravangian the best way he's found to augment the Diagram.
Hopefully, Moelach hadn’t decided to slumber again. The Death Rattles had, so far, offered them the best way that they’d found to augment the Diagram.
If Moelach is indeed another of the Unmade, isn't it worrisome that Taravangian’s hope to "save humankind" is being guided by a Splinter of Odium?
There is one you will watch. Though all of them have some relevance to precognition, Moelach is one of the most powerful in this. His touch seeps into a soul as it breaks apart from the body, creating manifestations powered by the spark of death itself.
–From the Diagram, Book of the 2nd Desk Drawer: paragraph 15