[Keeper of Dol Guldur]

See now, the bridge seen may have seemed a tad hellish with a fallen spirit present and flames erupting forth from fissures, but once old Durin's Bane heard Gandalf's intimidation game and quenched his own fires, it was nothing but black, and I'd say Gandalf was the only light source in the chamber (save for maybe Sting). It's true, you can't fight fire with fire . . .

Speaking of which, once the Balrog hit the lake, it went slime-form. In slime-form, it eluded Gandalf all the way to Zirak-Zigil. I hate to recall a point, but it didn't rekindle until it was out of the dank, dark tunnels, and in the sunlight. That sort of gives the idea that either, the Balrog could draw on any heat source to light itself into fiery wrath, or that the Sun was scorching it's shadowy mantle and doing half Gandalf's work for him . . . if the Balrog was the one who led Gandalf to the peak, chase or no chase, it wouldn't be a smart move if it couldn't withstand the light of day. Anyway, Gandalf seemed to think it was the first point, the Balrog used sunlight to flame anew, and so the whole point about sunlight hurting it stands as invalid.

And after all, it was Melkor's orcs that couldn't withstand the sun, weak miserable cave creatures, trolls, vampires, and the like. Those were things he had some part in creating. The Valaraukar, he did not create. All he did was give them each a little of his power, the ability to wreath their fiery spirits in a cloak of shadows. While I still think the Flame of Anor is referencing the Ring of Fire, I tend to lean toward the idea of it being an ancient elf-weapon.

After all, the Balrog may not have been awake during the forging of the Rings of Power, but living in Moria, if he ever learned to read Dwarven he'd likely come to find out about the bustling trade and feats of the neighbors in Eregion. As a matter of fact, he'd likely be pretty interested in the movements of the Noldor who lived so close to his domain.

And lastly, if by mentioning his service to the Secret Fire, Gandalf was trying to let the Balrog know his fight was not with it (being a creature of a time long past), he seems to me to maybe have been saying; "I have no business with you, I'm on an urgent errand from the Gods who even you don't have the gall to challenge." All it took to intimidate the orcs was his tone. Wielder of the Flame of Anor may have indicated his status as elf-friend and one of the Wise, one of the most powerful beings around, and then he gave a direct order. By saying, "the dark fire will not avail you", I think Gandalf was simply saying, "I'm not intimidated by your little show of force, bursting into flame and spreading your shadow out." (which reminds me of a cobra as far as spreading out to look bigger). Then Gandalf says, "go back to the shadow". It's not like he's saying, "go back to the abyss prepared for you and your master." I think he was just telling the Balrog to go back downstairs, get it's *** back in bed and don't get in the way.

Now, during the integral mission, was not the time or the place for the Balrog to go on with it's master's ancient feuds. But apparently, the Balrog couldn't have cared less about Gandalf's little mission, and wouldn't have minded knowing what a motley group of men, dwarf, elf, and little folk were doing with some powerful and dark heirloom, and a handfull of powerful and elvish ones.

So naturally, when it decided to step forward, it did it slowly. Boromir blew his great horn and it stopped, probably wondering if the warriors were going to rush in and aid Gandalf in a fight. In any case, Gandalf didn't want them involved. He knocked the bridge right out from under foot, the Balrog fell, but was intent to take Gandalf out with it, pulled him down via whip, and the fight was on.