Disrupting Shoal
Instant — Arcane
You may exile a blue card with mana value X from your hand rather than pay this spell's mana cost.
Counter target spell if its mana value is X.
Scott M. Fischer
Ultimate Masters (UMA)
• #51Rulings
If a card in your hand has {X} in its mana cost, X is considered to be 0.
(wotc • 2018-12-07)
If a spell has {X} in its mana cost, include the value chosen for that X when determining the mana value of that spell, even if it was cast for an alternative cost and no mana was spent on X.
(wotc • 2018-12-07)
Disrupting Shoal can target any spell, but does nothing unless that spell's mana value is X.
(wotc • 2005-02-01)
Rulings
If a card in your hand has {X} in its mana cost, X is considered to be 0.
(wotc • 2018-12-07)
If a spell has {X} in its mana cost, include the value chosen for that X when determining the mana value of that spell, even if it was cast for an alternative cost and no mana was spent on X.
(wotc • 2018-12-07)
Disrupting Shoal can target any spell, but does nothing unless that spell's mana value is X.
(wotc • 2005-02-01)