Spells don't trigger Heroic. Heroic is triggered by the permanent that has it being the target of a spell. Subtle difference, but relevant here.
Each permanent with heroic that is the target of a spell will have their heroic ability trigger. Dauntless Onslaught targets two creatures, if they both have heroic, both of their abilities will trigger.
June 26, 2014 4:04 p.m.
Dauntless Onslaught is just one spell, but the triggered abilities of Akroan Skyguard and Phalanx Leader are two separate abilities, and it's fine for different triggered abilities to all trigger from the same event. Both Heroic abilities trigger in your example.
This is one of the main reason why cards like Dauntless Onslaught and the Strive mechanic were put into Theros block, to be great with Heroic!
June 26, 2014 4:05 p.m.
Devonin: I get what you're trying to say, but it's not right. Spells do trigger Heroic abilities, because that's what the abilities say ("Whenever you cast a spell that targets...").
June 26, 2014 4:07 p.m.
Well, I mean, I feel like in the strictest sense it is right. The trigger condition for Heroic is "This permanent becomes the target of a spell cast by its owner"
Yes, you need to cast a spell in order for that condition to ever be met, but the distinction between "the spell doesn't trigger it" and "it triggers itself when it becomes the target of the spell" was stated in the name of making clear that one spell can cause any number of Heroic abilities to be triggered as long as each permanent with a Heroic ability is being targeted. The source of the trigger is the card, not the spell targeting it.
I can see how the phrasing might seem awkward though.
June 26, 2014 4:48 p.m.
The phrasing is very important for making sure the explanation is correct. For example, Heroic doesn't trigger when the creature "becomes the target of a spell cast by its owner", because that would allow for target-changing effects to trigger the ability (as-is, they don't). The trigger condition is exactly what the printed/Oracle text of the cards already says, and for relatively simple cards like these there's no need to restate the text in a different way to get a point across. You can just take it as it is, avoiding the type of confusion that can appear when a card says one thing but an explainer says another.