An Armagi is a dangerous creature that appears if The Phase cannot be completed. They can transform between a normal Styx and an Armagi. If an Armagi is stunned then it will turn into a Styx for a short period of time. The Armagi have the ability to heal amost instantly once they are wounded. If an Armagi is not blown up (the only way to kill one), then it will continue to thrive and create more Armagi- obviously not a good thing. Armagi can adapt almost instantly for terrains of water, ground, and air.
Armagi are made out of a clear jelly-like substance, that can instantly evolve depending on the terrain that the creature has to travel through. If the Armagi needs to fly, it will generate wings. If it needs to swim, it will grow fins. Of course, if it needs to walk, then it will use its feet.
In the series Edit
In the epilogue of Spiral, Rebecca Two is mourning her sister's death when the Old Styx calls her to the swimming pool. She sees coccons and hatched Armagi swimming in the water. But this only occurs in the Epilogue.
In the final book, the Armagi and Styx rampage across England. The country is in chaos and many citizens are killed by the Armagi. Parry and his men capture one in Styx form and study it in a military laboratory. While running electrical currents through it, it turns into its monster form and causes an evacuation. Parry kills it with a burn-out fire wall, incinerating it. Another Armagi almost kills Chester, but Martha appears and kills it with her crossbow. She then summons a group of Brights which she tamed, and the creatures rip another Armagi to pieces. A mob group in Norfolk destroy two Armagi using a car bomb. After leaving David's house, Elliott coats Will's body with her blood and that allows them to get past Armagi-filled houses without being heard or smelled. During the battle at the end, the Armagi surround St. Paul's Cathedral with Elliott inside. However, much to Alex's surprise, they don't attack her. Elliott explains that she is a Styx like the rest of them, and reveals that the Styx are aliens from the inner world. She says that the Styx at one point looked like the Armagi, but evolved to look like humans. After slamming the trident down, the Armagi disintegrate like dead fish and all of them are killed.
Later, during the clean-up operation, the French government thinks the Armagi were mutant species created by British subterranean nuclear testing.