SIEGE PERILOUS
A circle of stones. A portal of escape. A precious stone. A magic mirror.
A seat for a knight.
But always a journey of the self.
The Siege Perilous is a mutable artifact that imparts profound and personal change on any mutant who travels through it. While the Siege itself takes various forms, utilizing the Siege typically involves entering it in some way -- through the glass of a mirror or a gem expanded to the size of a doorway, for example.
The Siege Perilous of mutantkind differs slightly from the Siege Perilous referenced in Arthurian literature, though they may be connected. In those stories, the Siege is not itself the goal but Merlyn's reward for the Knight of the Round Table who acquires the Holy Grail. These, however, are legends at best.
Upon exiting the Siege Perilous, a mutant finds themselves fundamentally altered in some way -- be that through partial or total amnesia, temporal or geographical displacement or intensely personal dreamlike visions. Many report a brief sense of ego death followed by a gradual confrontation with the self leading to reconciliation.
During her leadership of the X-Men, Betsy Braddock utilized the Siege as an escape route for her team, ultimately saving their lives, but with unpredictable results. Few know more about the Siege, its magic and its dangers, than her.
"Know, X-Men, that the Siege Perilous is for your use as well. As AVALON was for King Arthur, so may the Siege be for you."