User blog comment:ImperiexSeed/ARCHANGEL or LEVIATHAN!/@comment-213828-20120513212716/@comment-3045936-20120513213413

I said it too and I cannot say one way or another. After all, maybe Castiel doesn't know if the Levianthans can kill the Archangels and just all other classes or believes that if they can kill normal angels why not all classes. But, I find it odd. This is one possible theory after seeing that. Maybe, Levianthans can even turn off Archangel's powers. But, if they could use them on Levianthans they might be able to kill them. Like why they didn't have Sam and Dean use Death's Scythe to kill Lucifer. Even though it can kill the Archangels it requires them to directly use it on them like the Demon-killing knife. If you cannot use it despite it workable on the problem its useless to use.