Counter target spell. If the amount of mana spent to cast that spell was less than its mana value, you draw a card.
For spells with
in their mana costs, use the value chosen for X to determine the spell’s mana value.
The mana value of a spell isn’t changed by alternative costs, cost increases, or cost reductions. For example, if you cast Thrumming Hivepool (an artifact with affinity for Slivers), its mana value is 6 no matter how many Slivers you controlled when you cast it.