2005-02-01 : Disrupting Shoal can target any spell, but does nothing unless that spell’s converted mana cost is X.

2018-12-07 : If a card in your hand has {X} in its mana cost, X is considered to be 0.

2018-12-07 : If a spell has {X} in its mana cost, include the value chosen for that X when determining the converted mana cost of that spell, even if it was cast for an alternative cost and no mana was spent on X.