When an archaeologist is killed by a god, a student in mythology finds out and goes on the journey to find the weapon that can kill gods, a grotesque monster made back by a medieval monastery father.

Well, I wanted it monster vs monster/god. I guess I should have logged it under SCI-FI rather than Action.

Agree with previous comments. Without some connection between the student and the archaeologist there is no purpose for the protagonist. I like the idea of the weapon being an ancient item/monster but I see an inhabitant of ?medieval monasteries (which, if you're referring to Medieval England, were all Christian I believe) as only believing in one God. Maybe consider a different creator? Perhaps the item/monster is held by the descendant of its creator and that person could help/hinder the student on his quest?

When an ancient God hellbent on world domination takes over his father's body, a mythology student must track a secret society to get the only weapon that can defeat a deity.
Having the ancient God taking over his father's body rather than kill doubles the tension while still keeping it personal.
Can he save his dad? And if he can't ?can he kill him?