In the Eye of Chaos

World Enchantment, 2U (3)
Whenever a player casts an instant spell, counter it unless that player pays {X}, where X is its converted mana cost.¹
Illus. Brian Snõddy

Gatherer Card Rulings [Nov 2009]

• 10/4/2004: This ability triggers when the spell is cast.
• 10/1/2008: This has the supertype world. This supertype is similar to legendary. The difference is that when a world permanent enters the battlefield, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter the battlefield at the same time, they're both put into their owners' graveyards.

Format Legality	Legal in Vintage, Legacy Banned in Extended, Standard
Printings (1/2)	Legends (Rare)