I want to know when Kaalia of the Vast ability triggers is it when I declare it attacking or when it hits a player opponent. I feel it's way to overpowered if its when I declare her attacking because of cards like dread cacodemon. Either way I'd like a clear answer so I can stop yelling at my friends
"When [this] attacks" triggers trigger on the creature being declared as attacker in the declare attacker step's turn based action. So Kaalia of the Vast puts out the other creature before blockers are declared. Dread Cacodemon isn't cast via Kaalia's trigger, it is just put on the battlefield. So its ablity doesn't trigger. Also, a "when [this] attacks" trigger of any creature put out this way won't trigger either, because you never declared it as attacker.
Former Rules Advisor
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