User blog comment:ImperiexSeed/ARCHANGEL or LEVIATHAN!/@comment-149.210.105.71-20130514175442/@comment-25358468-20130514181045

I think it's doubtful Lucifer could kill a Leviathan. They overpowered Castiel when he was carrying the souls, and remember, with the power of those souls he obliterated Raphael, also an Archangel.