Gandalf's Staff

[Nilpaurion Felagund]

Gandalf may have been stalling for time to gather energy for his blast (note all of his huffing and puffing about immediately prior to the incident). (Kuru)

Here we can reach a sort of compromise. Perhaps Gandalf was attempting to scare the Balrog off while preparing for a blast, should it come (which it did).

Re worms:

First of all, I don't think the Balrog was under any command. Like the dragons. Sauron can attempt to ally with it, but not command it.

The Balrog could be after the Ring. It doesn't have to understand its pull to be drawn by it (like, as Kuru said, the Watcher did). Although the puzzle that is Gandalf would be a better reason. Who is this being mighty in magic that dares to come in my abode? the Balrog might be thinking ever since their powers met at the Chamber door.

As for the Balrog and sunlight, well . . .