I have no idea what cabal or class this might fit with, but it seemed cool at the time.

First, consider classic forceduel. Caller and target are transported to some magical place where they fight to the death. Sounds great. Except classes received it whose main problem is keeping people in combat. Paladin and Invoker come to mind. It could be argued that truly honorable combat takes place between equals, not between an over-geared, over-prepped power class and some poor shmoe who happened to type "quaff return" a split second too late.

So equal the playing field. Both are transported to the same magical place, only in my version the caller becomes a mirror immage of his target for the duration of the fight. That includes race, class, stats, skill%s, worn gear, inventory, affects, cabal powers, etc. The only difference I'd suggest is that if the caller and target share a common skill/spell/song/commune then the caller keeps his skill% instead of inheriting the target's.

End result: the caller can't rely on class imbalance, preps, or gear to ensure victory. He has to win by skill and skill alone, since he and his prey are basically identical.

If the caller dies then all mimicked possessions disappear and his corpse contains whatever he carried before combat began.