Repeal

• WWizards of the Coast2021-03-19
  Official Ruling
  The mana value of a token that isn't a copy of another object is 0. A token that is a copy of another object has the same mana cost as that object.
• WWizards of the Coast2021-03-19
  Official Ruling
  If a permanent on the battlefield has in its mana cost, X is considered to be 0.
• WWizards of the Coast2021-03-19
  Official Ruling
  If the target permanent is an illegal target by the time Repeal tries to resolve, the spell doesn't resolve. You don't draw a card.

Rulings via Scryfall