a quick note about cowl. We know that he used/uses necromancy not only from the dark stain harry feels, but because he was there at the darkhallow. remember that u had to be protected by necromancy magic in order to get close. Ramirez got there without using necromancy because he was riding Sue, which probably 'trailed' a huge necromancy wake, like a boat in the water. Its plausable that Cowl sneaked into the gathering, but he would have to be really really close to the other zombies. Maybe in the middle of a huge crowd of zombies would give him enough protection. But most likely not. Its most likely that he had his own 'field' of necro energy surrounding him.