The Headhunters are the undead heralds of the Anti-Moderator. They are more or less indescribable.
Powers and Abilities
The Headhunters are nearly unstoppable creatures of primal rage, with superhuman strength and speed. Like other Elder Spawn, they have a deleterious effect on the mental health of humans and human-level sentient beings, especially for those who are unprepared, weak-willed, and/or highly rigid in their thinking, and their gaze can sap their victims' wills and plunge them into despair. Their presence tends to impair the functioning of lights and other electronic devices.
The Headhunters created from the people of the dead Earth of Hell's Titans (perhaps in addition to other worlds that were destroyed or exiled from continuity) by the Anti-Moderator, using the anti-narrative energy of The Hungry Past.
Most of them were re-killed by Ultimate wReam, but one – the one sent to capture Ultimate Mercenary – survived due to being trapped in Limbo. It was captured by the Crossover Queen to use as a conduit for the Hungry Past, but UM used the Power Kirby to restore its humanity, revealing her to be Manga Girl II.
Later, when Professor Penumbra attempted to return Ultimate Mercenary to his own world from Earth-20, he accidentally summoned a Headhunter which was the counterpart of Kid Enthusiastic. They defeated the creature and imprisoned it in a trap built by Penumbra and Kid Enthusiastic-20. Since Hell's Titans branched off the original Looniverse in 1997, and Kid Enthusiastic didn't exist there until 2002, UM speculated that someone or something was creating new Headhunters. This has not yet been followed up on...