[pyan]

Originally Posted by Rinion

Gandalf's power has been measured against Durin's Bane, the "strongest and foulest of Sauron's minions",

And died!
"Naked I was sent back- for a brief time, until my task is done"

If he was sent back, surely this means there was something more powerful that Gandalf himself to do so. - this can only have been Iluvitar himself - who normally would not intervene.

Gandalf really 'died', and was changed: for that seems to me the only real cheating, to represent anything that can be called 'death' as making no difference... He was sent by a mere prudent plan of the angelic Valar or govenors; but Authority had taken up this plan and enlarged it, at the moment of its failure. 'Naked I was sent back- for a brief time, until my task is done'. Sent back by whom, and whence? Not by the 'gods' whose business is only with this embodied world and its time; for he passed 'out of thought and time'.

: Letters - 156

My point is that the Balrog was as powerful, at least, as Gandalf.