Lets say I have Kaalia of the Vast on the battlefield. I attack with her, and cheat out Aurelia, the Warleader or Tyrant's Familiar. Would I get their "on attack" trigger? Or are they skipped.
4 Answers
No, you don't get the "on attack" trigger.
One of the rulings on Kaalia covers this point:
The creature card is already tapped and attacking as it’s put onto the battlefield. Any abilities that trigger when a creature becomes tapped or when a creature attacks won’t trigger for that card.
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One should mention that this is in contrast to "whenever counters are placed" triggers, which in fact do trigger if a permanent enters the battlefield with counters on it Apr 11, 2019 at 10:51
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The opposite (kind of) situation is also true, though it's easier to illustrate Alesha, Who Smiles at Death. Her ability puts creatures with power 2 or less onto the battlefield tapped and attacking. This means that you can use her to attack with creatures with defender, since they are never declared as attackers. On subsequent turns they are still unable to attack.– John DoeApr 12, 2019 at 22:17
No, you don't get "on attack" triggers for creatures that enter the battlefield "tapped and attacking".
The reason is that being declared as an attacker is a single event that happens only once per combat, at the end of the "declare attackers" step of the combat phase. It's the event that triggers Kaalia of the Vast's ability in the first place, so by the time a creature is put on the battlefield as a result of Kaalia's ability, that point has already passed and cannot trigger the ability of Aurelia or Tyrant's Familiar.
- Declare Attackers Step
508.1. First, the active player declares attackers. [..]
[..]
508.1m Any abilities that trigger on attackers being declared trigger.
508.1m is when Kaalia's ability triggers. It goes on the stack afterwards:
508.2. Second, the active player gets priority. (See rule 116, "Timing and Priority.")
508.2a Abilities that trigger on a creature attacking trigger only at the point the creature is declared as an attacker.
508.2b Any abilities that triggered on attackers being declared or that triggered during the process described in rules 508.1 are put onto the stack before the active player gets priority; the order in which they triggered doesn't matter.
Kaalia's ability goes on the stack now, eventually resolves, and a creature is put on the battlefield tapped and attacking. That creature never sees the end of the "declare attackers" step described in 508.1m and therefore does not trigger its own "on attack" ability.
"Creature attacks" is short for "declared as an attacker".
The creature wasn't declared as an attacker, so their triggered ability doesn't trigger.
According to the Comprehensive Rules:
508.4 If a creature is put onto the battlefield attacking, its controller chooses which defending player or which planeswalker a defending player controls it’s attacking as it enters the battlefield (unless the effect that put it onto the battlefield specifies what it’s attacking). Similarly, if an effect states that a creature is attacking, its controller chooses which defending player or which planeswalker a defending player controls it’s attacking it becomes attacking (unless the effect has already specified). Such creatures are “attacking” but, for the purposes of trigger events and effects, they never “attacked.”
So "Whenever CARDNAME attacks" triggers don't, and "CARDNAME attacked" doesn't.