Oracle Text

Destroy target artifact or enchantment with converted mana cost 4 or less.

Card Rulings

9/20/2016 If a permanent has in its mana cost, X is considered to be 0.
9/20/2016 The converted mana cost 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.