376. Triggered Abilities are repeatable effects that happen when a Condition is met.

376.1. Triggered Abilities can usually be recognized by the word "when" followed by a game action or event; the word "at" followed by a point in time during the turn sequence; or the phrase “the [Nth] time” followed by a game action or event. Examples: " When you conquer here, you may spend a buff to draw 1." "At the end of your turn, ready 2 runes." “The first time I move each turn, you may ready something else that's exhausted.”

376.1.a. The phrases that identify triggered abilities do not always appear at the beginning of sentences or abilities.
376.1.b. If an ability triggers “the [Nth] time” something happens and that trigger condition is met multiple times simultaneously, the ability’s controller picks one of those instances to serve as the trigger condition. The ability triggers only once, due to the chosen condition. Example: Wraith of Echoes reads “The first time another friendly unit dies each turn, draw 1.” That ability hasn’t triggered yet this turn. Two other friendly units die simultaneously (say, due to combat damage). The Wraith’s controller chooses one of those deaths to trigger Wraith’s ability.

376.2. Triggered Abilities have a Condition and an Effect.

376.2.a. The Condition follows the When.
376.2.b. The Effect is the Instruction that follows the comma after the Condition.
376.2.c. The Condition of a Trigger is evaluated after a potentially inciting event has been processed.
376.2.c.1. If a Game Object with a Triggered Ability that is active in a specific zone, it is evaluated and subsequently triggered if it enters that zone at the same time that its Trigger ’s condition is met. Example: Immortal Phoenix says “When you kill a unit with a spell, you may pay [1][C] to play me from your trash.” This ability triggers if Immortal Phoenix is in your trash immediately after you kill a unit with a spell, even if the unit you killed with a spell was that Immortal Phoenix.
376.2.c.2. A Game Object will not be able to successfully be able to evaluate its Trigger Condition , however, if it leaves the zone that its Trigger is active from at the same time that its Trigger is satisfied. Example: Viktor, Leader says “When another non-Recruit unit you control dies, play a 1 [M] Recruit unit token into your base.” This ability triggers if Viktor is on the board immediately after another non-Recruit unit you control dies. It does not trigger if Viktor and another non-Recruit unit you control die during the same game action (for instance, if they are both killed in the same Cleanup due to the damage dealt by Unchecked Power).

376.3. When a Condition is met, a Triggered Ability behaves like an Activated Ability and is placed on the Chain.

376.3.a. Triggered Abilities can be put on the Chain during Closed States or Open States on any player's turn.
376.3.b. If more than one Triggered Ability is Triggered simultaneously, then the player that controls the Abilities selects the order to place them on the Chain.
376.3.b.1. If multiple players separately control Triggered Abilities that are Triggered simultaneously, then starting with the Turn Player and proceeding in Turn Order , each player orders their Triggered Abilities on the Chain.

376.4. Some Conditions are commonly used and structured in a way that explicitly defines their use and other properties of the Effect that is associated with it.

376.4.a. Play Effects are Triggered Abilities with the Condition that the Permanent that has the Play Effect being played to the board.
376.4.a.1. These are commonly structured as “When you play me…” for Units and “When you play this…” for Gear.
376.4.a.2. These Triggered Abilities are put on the Chain as Pending Items after the Permanent these effects correspond to is finalized and enters the board.
376.4.a.3. These Triggered Abilities can be referred to as Play Effects.
376.4.a.4. Abilities that trigger when another object is played are not considered Play Effects.
376.4.b. Conquer Effects are Triggered Abilities with a Condition of a Unit participating in, and successfully Conquering a Battlefield.
376.4.b.1. These are commonly structured as “When I conquer…” and “When you conquer…”
376.4.b.2. This category of Triggered Abilities encompasses only those that are triggered from Units that were present during the Conquer action, or Abilities that reference the player that performed the Conquer action. 376.4.b.2.a. The Conquer Abilities of Units are put on the Chain as Pending Items after the Unit(s) these effects correspond to are present at a Battlefield when a player gains control of it and gains 1 Victory Point from Conquering. 376.4.b.2.b. The Conquer Abilities of anything that references the player Conquering is put on the Chain as a Pending Item when the Condition that the player that controls the triggering source has performed a Conquer and gained 1 Victory Point. 376.4.b.2.c. If the act of gaining one point from Conquering is negated or replaced in any way, the Conquer Effect will still trigger.
376.4.b.3. These Triggered Abilities can be referred to as Conquer Effects.
376.4.c. Hold Effects are Triggered Abilities with a Condition of a Unit being present at a Battlefield during the Beginning phase when a player scores Victory Points from Holding.
376.4.c.1. These are commonly structured as “When I hold…” or “When you hold…”
376.4.c.2. This category of Triggered Abilities encompasses only those that are triggered from Units that were present during the Hold action, or Abilities that reference the player that performed the Hold action. 376.4.c.2.a. The Hold Abilities of Units are put on the Chain as Pending Items after the Unit these effects correspond to are present at a Battlefield when a player maintains control of it and Gains 1 Victory Point during their Beginning Phase from Holding. 376.4.c.2.b. The Hold Abilities of anything that references the player Holding is put on the Chain as a Pending Item when the Condition that the player that controls the triggering source has performed a Hold and gained 1 Victory Point. 376.4.c.2.c. If the act of gaining one point from Holding is negated or replaced in any way, the Hold Effect will still trigger.
376.4.c.3. These Triggered Abilities can be referred to as Hold Effects.
376.4.d. Attack Triggers are Triggered Abilities that trigger when a Unit gains the Attacker designation for the first time during a combat.
376.4.d.1. These are commonly structured as “When I attack…”
376.4.d.2. These Triggered Abilities are put on the Chain as Pending Items after the Unit these effects correspond to gains the Attacker designation during Combat . 376.4.d.2.a. These triggers can only become fulfilled once per combat, despite a Unit being able to gain and lose the Attacker designation multiple times in the same combat.
376.4.d.3. These Triggered Abilities can be referred to as Attack Triggers.
376.4.e. Defend Triggers are Triggered Abilities that trigger when a Unit gains the Defender designation for the first time during a combat.
376.4.e.1. These are commonly structured as “When I defend…”
376.4.e.2. These Triggered Abilities are put on the Chain as Pending Items after the Unit these effects correspond to gains the Defender designation during Combat . 376.4.e.2.a. These triggers can only become fulfilled once per combat, despite a Unit being able to gain and lose the Defender designation multiple times in the same combat.
376.4.e.3. These Triggered Abilities can be referred to as Defend Triggers.