Event Horizon is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Nonbasic lands are Wastes. Whenever you tap a permanent for , add an additional . Whenever chaos ensues, choose one — • Draw four cards. • Destroy target permanent. • You may return target creature card from your graveyard to the battlefield.