Understanding: Why is Spark Double triggering enter the battlefield abilities of the copied creature?

Question

Spark Double reads:

You may have Spark Double enter the battlefield as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it’s a creature, it enters with an additional loyalty counter on it if it’s a planeswalker, and it isn’t legendary if that permanent is legendary.

If I decide to copy a creature with an ETB-effect, like Dreadhorde Twins, why does Spark Double also trigger the copied ETB-effect? Its own ETB-effect is, that it may enter the battlefield as a copy of a creature, does that mean, its own ETB-effect is always resolved first?

Answer 1

Spark Double triggers the copied creature's ETB effects because its copy ability works as a replacement effect, not as its own ETB ability. On the battlefield, there is no time when the game sees the non-copied version of Spark Double, and copied creature's ETB's can trigger as they would on the original.

Spark Double's copy ability and the other modifications (counters, non-legendary) are replacement effects:

614.1c Effects that read "[This permanent] enters the battlefield with . . . ," "As [this permanent] enters the battlefield . . . ," or "[This permanent] enters the battlefield as . . . " are replacement effects.

That means if you choose to copy a creature or planeswalker, the game does not see the non-copied Spark Double enter the battlefield, but only the copied creature/planeswalker:

614.6. If an event is replaced, it never happens. A modified event occurs instead, which may in turn trigger abilities. [..]

The event to be replaced is the Spark Double entering as a 0/0 creature, which is the consequence of a creature spell resolving. That means all applicable ETB triggers will happen, whether they are on the copied creature, or on other sources that apply to the copied permanent entering.

Hypothetically, the only way that the copied creature's ETB's would not go off was if the copy ability itself was an ETB. If Spark Double would copy a creature as e.g. an ETB or activated ability, it would be too late to trigger the copied creature's ETB's. Also, practically speaking, the copy ability could not be its own ETB, because if Spark Double entere the battlefield as a 0/0, it would generally die to state-based actions before it could assume its copied form.

Answer 2

Spark Double's ability is not an enter the battlefield trigger but rather an enter the battlefield replacement effect. When a creature enters the battlefield, there are two quanta of time. The first is the moment that it enters the battlefield, and the second is the moment after. Replacement effects happen at the moment that the creature enters the battlefield, whereas enter the battlefield triggers happen at the moment immediately after that. Thus, Spark Double gains the ETB trigger before triggered abilities are checked.

This difference is both visible and notable in terms of when choices are made. Replacement effects need their choices made before the permanent enters the battlefield whereas triggered abilities have their choices made after.

Here are the relevant rules for all of the above:

614.1c Effects that read "[This permanent] enters the battlefield with ... ," "As [this permanent] enters the battlefield ... ," or "[This permanent] enters the battlefield as ... " are replacement effects.

614.12a If a replacement effect that modifies how a permanent enters the battlefield requires a choice, that choice is made before the permanent enters the battlefield.

614.6. If an event is replaced, it never happens. A modified event occurs instead, which may in turn trigger abilities.

603.6a Enters-the-battlefield abilities trigger when a permanent enters the battlefield. These are written, "When [this object] enters the battlefield, ..." or "Whenever a [type] enters the battlefield, ..." Each time an event puts one or more permanents onto the battlefield, all permanents on the battlefield (including the newcomers) are checked for any enters-the-battlefield triggers that match the event.

603.3. Once an ability has triggered, its controller puts it on the stack as an object that's not a card the next time a player would receive priority.

603.3d The remainder of the process for putting a triggered ability on the stack is identical to the process for casting a spell listed in rules 601.2c-d. If a choice is required when the triggered ability goes on the stack but no legal choices can be made for it, or if a rule or a continuous effect otherwise makes the ability illegal, the ability is simply removed from the stack.