Lilting Refrain

At the beginning of your upkeep, you may put a verse counter on this enchantment.
Sacrifice this enchantment: Counter target spell unless its controller pays {X}, where X is the number of verse counters on this enchantment.

World Championship Decks 2000

Urza's Saga

During your upkeep, you may put a verse counter on Lilting Refrain.
Sacrifice Lilting Refrain: Counter target spell unless its caster pays an additional o
X, where X is the number of verse counters on Lilting Refrain. Play this ability as an interrupt.

Adding a counter is optional. If you forget to add one during your upkeep, you cannot back up and add one later.