User blog comment:Hitsuji Mamoru/FGO-style Servant Creation Room/@comment-4802891-20170203204649/@comment-4802891-20170204135309

Oh i see.

Well, Tolkien isn't that potent. He can change rules of the World to those of his world, but he can't achieve miracles that aren't meant to be.

For example, since he is a Caster, his traits would change to those of the Maiar (Gandalf's race) inside Limited Legendarium. Someone like Artoria would be a mere human and Excalibur would be considered a powerful sword with a possibly deep history. Enuma Elish or Rhongomyniad, linked to the World itself, would be ineffective because the Silmarillion doesn't aknowledge them as part of its myth.

He CAN'T decide on a whim that Excalibur is suddenly capable of slicing dimensions, or make himself a fire-breathing dragon. He isn't God, just the conpendium of his own world. He can't even summon his Noble Phantasm because it would expand across the planet AND time, both past and future. No single creature on this planet (aside from Shiki) would have enough energy to use such a powerful magic. That's why he needs the Grail, and a way to reach the Root to alter its genesis itself... I'm sure that's impossible but the Planet won't gamble on that and send a Counter Guardien to kick his ass before he could even attempt anything.