[quote=@Melkor]
So it's more like summoning a familiar? What about the stipulation that two legendary creatures, with the same name, can't be on the field at the same time? Does that still apply? Or may I summon four Niv-Mizzets? Though, I guess it could take too much energy anyway - what if someone else summons the same legendary? - That's a better example.
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I'm not sure what you actually mean by summoning a familiar, so I can't comment on that. If I recall correctly, the flavor stipulation on Legendary creatures/artifacts/etc was that you're summoning an aetherial reflection of them, but there's still just one reflection out there to summon. This changed in the game for crunch reasons, but I'd like to keep that on in the game. Though I doubt there will be a situation in this game where the same legendary creature is being summoned by two different mages.
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A familiar is basically a spirit-like copy of something rather than the real thing. I see now that it is the copy half of it, which is what I was asking.