A leaves-the-battlefield ability is a triggered ability that triggers when a permanent leaves the battlefield. Unlike most triggered abilities, the conditions for triggering a leaves-the-battlefield ability are checked based on the state of the game before the event happens, rather than afterwards. A permanent is considered to leave the battlefield when it ceases to exist because its owner leaves the game, unless it's phased out.
Rules[ | ]
From the glossary of the Comprehensive Rules (April 12, 2024—Outlaws of Thunder Junction)
- Leaves the Battlefield
- A permanent “leaves the battlefield” when it’s moved from the battlefield to another zone, or (if it’s phased in) when it leaves the game because its owner leaves the game. See rules 603.6c and 603.10.
From the Comprehensive Rules (April 12, 2024—Outlaws of Thunder Junction)
- 603.6c Leaves-the-battlefield abilities trigger when a permanent moves from the battlefield to another zone, or when a phased-in permanent leaves the game because its owner leaves the game. These are written as, but aren’t limited to, “When [this object] leaves the battlefield, . . .” or “Whenever [something] is put into a graveyard from the battlefield, . . . .” (See also rule 603.10.) An ability that attempts to do something to the card that left the battlefield checks for it only in the first zone that it went to. An ability that triggers when a card is put into a certain zone “from anywhere” is never treated as a leaves-the-battlefield ability, even if an object is put into that zone from the battlefield.
From the Comprehensive Rules (April 12, 2024—Outlaws of Thunder Junction)
- 603.6d Some permanents have text that reads “[This permanent] enters the battlefield with . . . ,” “As [this permanent] enters the battlefield . . . ,” “[This permanent] enters the battlefield as . . . ,” or “[This permanent] enters the battlefield tapped.” Such text is a static ability—not a triggered ability—whose effect occurs as part of the event that puts the permanent onto the battlefield.