Little is said of the Maskers.
Perhaps it's magic. Perhaps it's high-tech. Perhaps it's a combo of both, or maybe it's just extremely good disguise work. But the Maskers can be ANYONE.
When the group first started, it was based from a single dimension, had limited resources, and like the Freemasons of our world, was generally thought to be an organisation devoted to the greater good. As time went by, the group grew, became more diverse, and considerably more powerful. Who could stop a political assassination perpetrated by the Maskers, who could be the Emperor's aide one minute, and then a well-known member of the aristocracy the next? Who could prevent any move they saught to make?
This wasn't an issue until the time of the schism.
Some two hundred years ago, a breakaway group, also calling themselves the Maskers, went rogue. These were the ones more inclined to the political assassination... or any other mercenary work they saw fit to. Within decades, the group largely went from undercover keepers of peace and prosperity, to thugs, brutes, and villains. Unfortunately, they shared the invisibility the original group enjoyed.
How do you stop someone who can look like ANYONE?
There was no apparent limit to the changes that they can make to themselves, given enough time. Male, female, of any race or creed or species. Masters of both disguise and impersonation, they were brutal and vicious, taking several worlds by force. Yet whenever one was killed, they reverted back to their natural form, whatever it was.. and they always had the tattoo of a laughing Harlequin mask emblazoned on their upper arm when they died.
Rumour tells of a meeting hall, greatest of them all, known as 'The Hall of Perilous Masks and Mirrors'. Escaped prisoners tell of a mirror before which all is as it truly is... and of mirrors that show horrible reflections of the gazer. Perhaps the mumblings of the mad... or perhaps something more.
So where do they fit into a world? There are several types of characters who can be Maskers. It could be a protagonist, a member of the original group, or at least the original doctrine, who seek to further the organizations original goals. Though no one outside of either group truly understands the technique the Maskers use, they can perform it upon anyone.. although to perform it upon one who is not a member takes a matter of hours. The change is very real though.. which simply adds to the mystery of it all.
Perhaps there is a cabal of Dark Maskers (the semi-official term for the breakaway group), seeking to take over a local government. Their reasons are their own, but greed, and lust for power can sway the hearts of many...
Or perhaps they do not appear at all, but are rather the secret mysterious masterminds behind the dark things that befall the protagonists. The Dark Maskers aren't especially fond of others who can move between dimensions, especially those who have any sort of organization at all. Truly, such an organization would be wise to find some way to verify their members...
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To be continued upon request.