1 Sept 2023
Will's activated ability can't reduce the amount of colored mana you pay for a spell. It reduces only the generic mana component of that cost.
1 Sept 2023
Will's activated ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.
1 Sept 2023
The value of X is determined only once, at the time Will, Scion of Peace's activated ability resolves.
1 Sept 2023
Will's activated ability counts the total amount of life you gained without taking into account any life you lost during that turn. For example, if you gained 3 life and lost 3 life earlier in the turn, the cost of white and/or blue spells you cast this turn will be reduced by {3}.