Magic
Evaluating Intelligence
Evaluating Intelligence looks like a curiosity: you stand in a town appraising the wits of whoever is nearby and muttering about it. At Grandmaster it stops being a curiosity and becomes a permanent, substantial increase to the damage of every offensive spell you cast, which makes it one of the best returns on an AFK skill in the game.
At 100 skill every offensive spell you cast lands 20% harder — permanently, and stacking with an Inscribed Spellbook. It is the best thing an idle town macro pays out in the game.