Can we do it? At the end of the day will we just go up to him at the end of third arc and throw some spells at him like usual without anything to help us and end him? Are We so strong that there is nothing, and I mean nothing, in the spiral that can defeat us?
There are already plenty of things in the spiral that can defeat us. Many battles require multiple wizards working together to complete. Obviously, like every game, the player must have a way to win. If it's impossible to win, no one would play.
As we are now Grandfather Spider would probably curb stomp us into the next week. While we have defeated Gods such as the Olympians, one of his children with the Rat and even an artificial Titan, Grandfather Spider is in an entirely different league. That being said our wizards seem to grow explosively stronger the more we face difficult opponents. By the end of this arc after defeating his children we might gain enough power to compete with him. On the other hand, it would not surprise me if we received help from some of the more benevolent Creation entities such as Grandmother Raven.
