Who would win in a fight between...

[Ainaserkewen]

But don't forget Arwen is some kind of reincarnation of luthien, I think it would be a hell of a fight!

Uh, Firnantoonion, actually Arwen isn't a reborn Luthien, Luthien is dead, gone, the only elf ever to leave the circles of the world.

How about Shelob vs. Balrog?

Obviously the Balrog would win because Shelob is big and fat and lazy. However Ungoliant would probably put up a better fight, though both of them would probably run away to their dark lords before the balrog could touch them.