|“||I summon you, Elyaas who swims in the midnight seas of eternally drowning souls, Elyaas who lurks in the shadows that surround Pandemonium, Elyaas who bathes in tears and plays with the bones of lost sailors.||”|
–Magnus Bane's summoning
In 1878, Elyaas was among the many blue demons summoned by Magnus in aiding Will Herondale look for the demon that cursed him. Magnus immediately realized that he made a mistake summoning him as he was not precisely as blue in person as he was in illustrations and sent him back.
Elyaas was once again summoned by Magnus in 2007 as a job for Caroline Connor of Pandemonium Enterprises. While waiting for Connors' return, Elyaas, after being summoned early in the day, was kept in his pentagram in Magnus' apartment, where it dripped slime and became more viscous as the day drew on. Elyaas listened in on Magnus' conversations and insisted on recommending gifts, such as a mixed tape and scented candles, for Magnus' boyfriend, Alec, making the warlock decide that he was even a worse roommate than Raphael Santiago.
When Connors finally returned and revealed that her employers intended to let the demon curse the mermaids of New York, Magnus annoyingly expressed disdain in his unnecessary summoning, offering to do something about the mermaids himself instead, despite the demon's eagerness. Disappointed, Elyaas, as Magnus sent him back, furiously told Magnus that Alec, being a Nephilim, will never truly love him, and that Magnus' father will eventually bring him to the Void with him and the other demons. His last word, however, was his continued suggestion that Magnus buy Alec scented candles.
Elyaas, like typical cecaelia demons, was an ugly and slimy being. Elyaas was mostly shapeless, like a blob, with a head like a human's, except with eyes set close together, his nose and mouth combined in a triangular slit. He had no arms, a short torso, and short and thick tentacles. He was covered in greenish-black slime and had a mouthful of slime, making him sound like a middle-aged man speaking underwater.