Rulings

• The ability triggers whenever any player (including you) casts a spell of any type.2009-10-01
• This has the supertype world. When a world permanent enters, 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 at the same time, they're both put into their owners' graveyards.2008-10-01
• This is not an additional cost, it is a triggered ability.2004-10-04