"It's easy to cry 'For glory!' and charge those who disagree with you. But it takes finesse to turn enemies into allies rather than corpses."

Will, Scion of Peace

Vigilance
{T}: Spells you cast this turn that are white and/or blue cost {X} less to cast, where X is the amount of life you gained this turn. Activate only as a sorcery.

Wilds of Eldraine

Wilds of Eldraine Promos

The value of X is determined only once, at the time Will, Scion of Peace's activated ability resolves.

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.

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}.

Will's activated ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.