The Shadow Core is a powerful, apparently demonic entity from an unknown location in the space-time continuum, and semi-frequently antagonises the members of the FAW team.
The Shadow Core's first appearance was in FAW II: Schizophrenic, where it appeared in Florida as an apparently invincible and (at the time) seemingly plot-unrelated foe which took a large amount of time for the group to actually defeat. Later on in the same game, it appeared again in search of a shadow stone in order to destroy the light stone next to its brain. It tortured Chris and some of the other group members, then proceeded to absorb a spaceship acquired by Unown earlier along with the dark stone, before absorbing almost every single member of the team. Among the first of these was Unown Entity, who quickly became corrupted by the influence of the Shadow Core until he destroyed a vest carried by Martin, which resulted in a black hole which simultaneously destroyed the Shadow Core's control realm and the Shadow Core itself.
The Shadow Core later appeared in FAW III: Death's Embrace, where it took control of Chris Crippler, transforming him into the Shadow Wolf. The latter then proceeded to collect elemental dragons from varying time zones, reforming them into an army of shadow dragons, which then launched an assault upon Hammerspace. When this assault failed, the Shadow Core started to disintegrate, in an effort to take the shadows of the Universe with it; by doing this, the light from the stars in the Universe would supposedly incinerate everything in it. However, the team successfully managed to prevent this from occuring, and the Shadow Core was then sliced into several hundred pieces, and its brain stored somewhere in Hammerspace. Meanwhile, several Shadow Core copies were fought and destroyed by Mega Z, the last of which caused the Black Death of the mid-1300's.
The Shadow Core was not seen again until the end of FAW V: The Nightmare Begins - it had apparently escaped from Hammerspace and regenerated its body through means of two humans with control over lightning, and had now allied with the Master, along with a plethora of other antagonists, including an army of alien beings known as the Strafers, but these were quickly dispatched by the Shadlean's mothership and the rest of the team's efforts.
Near the end of FAW VI: The Last, the Shadow Core successfully possessed the ex-god of the FAW universe, Matt, proceeded to torture Chris and his brothers, the former of which had been brought back to life after being killed off by Nightmare, then crashed a spaceship into Earth, sending everyone on the planet into a coma for the next five thousand years or so except for the Scarlanexx leaders, who had left just minutes before. For a while after that, it merely sent threats at the team and observed how they coped with them and other challenges.
In FAW VII: Prelude for the Prelude, the Shadow Core decided to directly take on the group once again. At first, it appeared in the guise of a Hypervention, along with three regular Ventions. Once these were destroyed, it took on its true form once again, and began using a time-controlling orb of some kind to alter events around it without affecting the space-time continuum. After it was discovered that Unown could use the orb as well (in the Shadow Core's own words, "only lords of time or anyone who masters time can get into it"), he discarded the use of such orbs, and instead chose to possess Chris, trapping his mind within his body, the latter of which becomes horribly mutated. After yet more battling, the Shadow Core transformed into an even more powerful form than before, which spoke entirely in Latin. Soon enough, Unown was teleported away from the group, and was forced to stop time in order to find them again over the space of what was an eternity for him, but literally no time at all for everything else. He then brought a Shadlean ship into existence above the Shadow Core, and the fight continued once more. At some point during this, Chris managed to free himself of his possession, and from there, damage was dealt to the Shadow Core until it fainted and apparently dematerialised.
The Shadow Core then disappeared from existence until New Year's Eve/Day of an indeterminate year, where something caused it to regain its good side. It communicated to the people of Earth one last time, then changed into a human form, apparently its actual true form, at which point it was revealed that it had been cursed with its demonic form by some unknown force. Whether it (now he) will return in future FAW titles is unknown as of yet.
The Shadow Core has had a variety of powers in its run. Most notably of these was its nigh-invincibility in its first appearance in the FAW series, as well as the ability to absorb sentient beings and even machines into a pocket dimension of its creation, gaining their powers and slowly taking control of them mentally. It has also had the ability to transform living creatures into evil, shadowy versions of themselves, fire beams of darkness at its opponents, and has even been shown to have enough power to possess and take control of the mind of a god, albeit with some difficulty at times. In its most recent appearance, it has been shown to have the ability to alter time without fear of causing a paradox, transform into an entirely Latin-speaking form, and once in this form, regrow lost body parts in any form it likes, even if said lost body part is its head.