クルル・バルデシオン

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

If a card in your graveyard has {X} in its mana cost, X is 0 for the purpose of determining its mana value.

Krile Baldesion'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.