Lui-qui-annonce-la-fin

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

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of It That Heralds the End). The mana value of the spell remains unchanged, no matter what the total cost to cast it was.