As illustrated in the Codex
Downworlders are supernatural beings and hybrid creatures who inhabit the Shadow World. Downworlder is the widely used term to refer to beings that are said to be part human and part demon, and are even said to be the demonic counterpart of Shadowhunters, who are part human and part angel. They include werewolves, vampires, warlocks and faeries.
Although demonic in origin and nature, Downworlders possess human souls and are counted as members of the human race by the denizens of Heaven.
Downworlders normally cannot bear runes. However, the Alliance rune created by Clary Fairchild can be applied on them, allowing them to share abilities with Shadowhunters. Daylighter Simon Lewis was also Marked with the Mark of Cain.
Every fifteen years, the Accords are signed between the Downworlders and the Clave, the Nephilim. According to the Accords, as long as the rules stated here are not broken, they can live in peace without bother and may even provide each other help when the need ever rises. Also, each of the four races have been accorded a seat on the Nephilim council as of 2007.
- Although once mentioned by Jace, it was never made clear if voudun zombies really existed and were counted as Downworlders or if it was a joke. According to notes between him and Clary, they do exist.