Magic the Gathering lingering spell effect

Question

I have a question about a card sequence.

Let's say I play an instant card that says "all creatures who dealt damage this turn return to owners hand" in my first main phase.

Then if my opponent flash summons a creature card in my second main phase that says "when this creature enters the battlefield do two damage to target creature/player", does that creature return to my opponent's hand because I played the instant spell card in my first main phase and it says this turn and my turn hasn't ended? Or does that effect of the spell resolve and the effects no longer affect subsequent events?

Answer 1

The wording "All creatures who dealt damage this turn return to owners hand" is a little off. You could find the virtually identical

Return all creatures that dealt damage this turn to their owners' hands.

"Return." There's no duration. It's something that happens there and then. When it resolves, all creatures that dealt damage earlier this turn are returned to their owners' hand. Creatures that deal damage latter will not be affected.

"That dealt damage this turn" is just a condition that specifies which creatures are affected.

Return all creatures <matching this condition> to their owners' hands.

While there are no existing card with the initial text, there are existing cards with the different conditions. For example, there's Part the Veil. It's an instant with

Return all creatures you control to their owner's hand.

If at a later time you gain control of a creature, it will not be returned to your hand. Only creatures matching the condition at the very moment the effect resolves are affected.

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There is a thing called continuous effect which can last beyond the source of the effect that created it. Some of them affect the objects that matched the condition when the continuous effect was created and some of them continually revise what objects they affect. Here are the examples associated with rule CR 611.2c:

Example: An effect that reads “All white creatures get +1/+1 until end of turn” gives the bonus to all permanents that are white creatures when the spell or ability resolves—even if they change color later—and doesn’t affect those that enter the battlefield or turn white afterward.

Example: An effect that reads “Prevent all damage creatures would deal this turn” doesn’t modify any object’s characteristics, so it’s modifying the rules of the game. That means the effect will apply even to damage from creatures that weren’t on the battlefield when the continuous effect began. It also affects damage from permanents that become creatures later in the turn.

Related Answer

Answer 2

In your example, the spell you played would have no affect on anything that happens after the spell itself it done resolving. If a spell were going to have a lasting effect as you describe, that spell would need to create what is called a "continuous effect."

611.1. A continuous effect modifies characteristics of objects, modifies control of objects, or affects players or the rules of the game, for a fixed or indefinite period.

In most situations, a card that creates such an effect will state a duration, such as "until the end of turn." So to get the effect you are thinking, a card would need to state "Until the end of the turn, whenever a creature deals damage, return that creature to its owner's hand."