Ya he dose but basicly the balrogs look like a mosquito to him. But the balrogs have power over shadow and fire they might be able to take any form. But Balrogs have a weakness. If there mane of fire is put out the die. But it is hard to put it out because it is so hot and it keeps regenerating. But ancalagon is just to big and it took like 50 egals and a bunch of elves in sky ships to kill him. Gothmog died by one elf and we headbuted him. But if you think about it Gothmog was hier in rank then ancalagon then that means he was more powerful then Ancalagon in the eyes of Morgoth. Even if Ancalagon is so dang huge I will trust Morgoth and say Gothmog would win.
wow, I forgot, it is said, in the war of wrath when Morgoth released his dragons even the Valar fleed from them. So I guess they can kill them some how. I vote Ancalagon then, one on one anyway. But it would be a close battle!