In some ancient civilizations the Wolf was a symbol of the underworld. In Egypt, the guardian of the dead was Anubis who was a wolf-headed god. The jackal portrayed as black was the symbol of both death and regeneration.
William is also the one who hid inside the suits and kidnapped and killed children, leading to the assumption that William Afton is The Purple Guy of FNaF 2 and 3 (he is killed at the end of the book when Charlie sets off the spring locks in his suit).
Zeref ultimately survived the attack as Natsu prepared to attack him once more but Zeref stopped him in order to finally reveal the truth. Zeref tells Natsu his full name is Zeref Dragneel and states he is Natsu's older brother.