The Dantalion is a kind of ghoul-type demon—demons that feed on the dead.
Dantalion demons are creatures made up of grayish, pulsing, jumbled internal organs, pus, and blood, and a single yellow, weeping eye. They are about the size of a large dog. Their mouth looks like a slick black tunnel lined with teeth beneath the bundle of organs. They are able to use their body as appendages, using these extensions to grab their victims.
They are considerably strong, able to physically pull grown humans and also able to withstand warlock magic, though this is also typical as most demons can only be dispelled with adamas weapons—basically weapons such as seraph blades that can only be used by Shadowhunters. When struck with other blades, the Dantalion's body would simply absorb the weapon and can shoot them back out.
In 2007, Catarina Loss found a Dantalion feeding on corpses at the morgue of the Beth Israel Hospital. Because all the Shadowhunters of New York had evacuated to Idris, she called the local groups of vampires and werewolves for assistance. She first contacted Malcolm Fade, who went to the leaders of the New York vampire clan and werewolf pack, Lily Chen and Maia Roberts, respectively.
Lily, Maia, and Bat Velasquez arrived with a large, warlock-strengthened cage. Lily was astonished by the demon's monstrous appearance. The Downworlders had difficulty vanquishing the demon because they had no weapons that could defeat the creature. They only managed to subdue it with Catarina's magic and Bat quickly locking it in the cage.
Lily saw this as an opportunity and took a video of the encounter to share with other Downworlders as proof that they needed the Nephilim and thus could not afford to side with Sebastian Morgenstern in the impending war. The demon then taunted them by saying that he did not expect Shadowhunters to last for long as Sebastian was going to attack Alicante the following day and would annihilate them.