Will, Scion of Peace
Legendary Creature — Human Wizard
Vigilance
: Spells you cast this turn that are white and/or blue cost 
less to cast, where X is the amount of life you gained this turn. Activate only as a sorcery.
"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."
Ryan Pancoast
Wilds of Eldraine (WOE)
• #218Rulings
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.
(wotc • 2023-09-01)
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}.
(wotc • 2023-09-01)
The value of X is determined only once, at the time Will, Scion of Peace's activated ability resolves.
(wotc • 2023-09-01)
Will's activated ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.
(wotc • 2023-09-01)
Rulings
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.
(wotc • 2023-09-01)
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}.
(wotc • 2023-09-01)
The value of X is determined only once, at the time Will, Scion of Peace's activated ability resolves.
(wotc • 2023-09-01)
Will's activated ability doesn't change the mana cost or mana value of any spell. It changes only the total cost you pay.
(wotc • 2023-09-01)