State-based effects are a series of conditions the game checks for any time a player would gain priority. If any of the following conditions are true, the necessary action is carried out, and the game checks all the conditions again.
The state-based effects listed under Rule 420 of the Comprehensive Rules are:
- If a player has 0 or less life, that player loses the game.
- If a player has 10 or more poison counters, that player loses the game.
- If a player has been required to draw a card since the last time state-based effects were checked, but could not because his or her library was empty, that player loses the game.
- If a creature has 0 or less toughness, put it into its owner's graveyard. (This is not a destroy effect.)
- If a creature has lethal damage (damage greater than or equal to its toughness) and has a toughness of 1 or greater, destroy it.
- If two or more permanents in play have the legendary supertype and the same name, put all such permanents into their owners' graveyards.
- If two or more permanents have the world supertype, put all except the one in play for the shortest length of time into their owners' graveyards. If there is a tie for which one has been in play for the shortest length of time, put all into their owners' graveyards.
- If an aura is attached to an illegal permanent, or not attached to a permanent, put it into its owner's graveyard.
- If an equipment is attached to an illegal permanent, unattach it from that permanent but leave it in play.
- If a permanent that is not an aura or equipment is attached to another permanent, unattach it from that permanent but leave it in play.
- If a token is in a zone other than in-play, it ceases to exist.
- If a copy of a spell is in a zone other than the stack, it ceases to exist.
- If a copy of a card is in a zone other than the stack or in-play, it ceases to exist.