The Scarlet Witch's House of M enabled Shadow King of Earth-616 to escape to an alternate reality, Earth-6141. Once there, he possessed their version of Professor X and then corrupted his team of original X-Men. He maintained constant telepathic contact and control over them and forced them to kill all the heroes of their world. The Scarlet Witch's Decimation Wave enabled the Shadow King to bring himself and his team to Earth-616 in order to gain revenge on those who had crossed him.
There was nothing much known about the Shadow X team, The fact that they were evil alternate reality counterparts to the original X-Men team and were lead by the Dark Professor X. Their first assault was foiled by the mutant singer named Alison Blaire aka Dazzler after she performed at a local night club.
They killed Dazzler though she managed to revive herself. Whether Shadow-X had anything to do about this was unrevealed. They were defeated by the newly assembled team, New Excalibur but recently resurfaced and came for revenge on the team. Later, they allied with New Excalibur to save the city from Albion and to get revenge against him. However, the Shadow X team was killed by Albion's forces.
Shadow X Team Roster