Abrupt Decay

• 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
  A spell or ability that counters spells can still target Abrupt Decay. When that spell or ability resolves, Abrupt Decay won't be countered, but any additional effects of the countering spell or ability will still happen.
• WWizards of the Coast2021-03-19
  Official Ruling
  If a permanent has in its mana cost, X is considered to be 0.
• WWizards of the Coast2024-04-12
  Official Ruling
  If you target a creature with ward, you may still pay the ward cost, but Abrupt Decay won't be countered even if you don't.

Rulings via Scryfall