Balrogs vs Elves

[the real findorfin]

How could Ecthelion and Glorfindel have possibly killed Balrogs. (even with eagle assistance)

1. Gandalf couldn't even do it in Moria. Although he had diminished powers he was still more powerful than an elf.

2. Balrogs are still Maia so how can they die. Like sauron they can only lose their forms so where do they go.