Triggered Abilities in Magic: The Gathering, Explained

A triggered ability is any ability that starts with the words 'when', 'whenever', or 'at'. It does nothing until a specific event happens, like a creature entering the battlefield, a player drawing a card, or the beginning of an upkeep. Unlike activated abilities, you never choose to use a triggered ability; it fires automatically when its trigger condition is met, whether you want it to or not.

When a trigger condition occurs, the ability 'triggers' but does not immediately do anything. Instead, the next time a player would receive priority, the ability is put onto the stack above whatever caused it. From there it works like a spell: players can respond to it, and it resolves when all players pass priority. This delay is why responses to triggers are possible at all.

Triggered abilities use the stack, so they can be responded to and can be countered by effects that counter abilities. When a trigger goes on the stack, its controller chooses any targets and modes at that time, not when it resolves. If a triggered ability needs a target and none is legal, it is simply removed from the stack and does nothing.

Some triggers contain an 'intervening if' clause, written as 'when/whenever/at [event], if [condition]'. This condition is checked twice: once when the ability would trigger, and again when it resolves. If the condition is false at either check, the ability does nothing. This is different from a target requirement and is a common source of confusion, because the ability simply will not go on the stack if the 'if' is false at trigger time.

If several abilities trigger at the same time, the active player (the player whose turn it is) puts all of their triggered abilities on the stack first, in any order they choose, followed by each other player in turn order doing the same. Because the stack is last in, first out, the ability placed on the stack last will resolve first.

This ordering matters when triggers interact. For example, if you control two creatures that each trigger 'whenever a creature enters, draw a card' and a third creature enters, you decide the order of your own two triggers, but both will resolve before priority passes. When opponents also have triggers from the same event, turn order determines who stacks first, but the active player always goes first.