Final answer:
In MTG, a missed trigger typically cannot target something that entered the battlefield after the trigger event. Triggered abilities should be executed at the time specified by words such as "when," "whenever," or "at," and changes in the game state, after the missed trigger moment, do not alter the original condition or target of that trigger.
Step-by-step explanation:
In the context of Magic: The Gathering (MTG), a missed trigger refers to a situation where a player forgets to implement the effect of a triggered ability at the time it should have occurred. According to the Comprehensive Rules of Magic: The Gathering, a triggered ability uses the words "when," "whenever," or "at" to indicate when the ability is expected to go onto the stack.
As a rule of thumb, once a trigger is missed, it usually cannot target anything that wasn't already in place or specified at the time the trigger should have occurred. When a trigger is forgotten, players can't retroactively make selections or targets based on new conditions or game states that have arisen since the time the trigger should have been executed.
In competitive play, the rules for missed triggers are enforced with particular attention to communication and game state, and a judge may be called to determine the proper course of action, which can depend on the level of the event and whether the trigger would be considered detrimental or beneficial to the player who missed it.