G'raha Tia, Scion Reborn

Alternative costs, additional costs, and cost reductions don't change a spell's mana value. Its mana value is still based on its mana cost.

For spells on the stack with {X} in their mana costs, use the value chosen for X to determine the spell's mana value.

G'raha Tia's last ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack.