I know it has been gone over before but the card "Besiegers of Dorne" has made me unclear on what exactly a triggered effect is. I think the thing I am hung up on is when a passive or keyword is considered to be a triggered effect. Also, is it fair to say that any "Any Phase:..." or "Challenges:..." ability IS a triggered effect?

Egg said:

This is all in the FAQ.

A triggered effect is one that initiates because a player says so. Sure, there are probably other play restrictions (especially with Responses), but even if all the play restrictions are met, if a player doesn't want a triggered effect to happen, it doesn't. And yes, 9999 times out of 10000, a triggered effect will be one that has a bold timing word in front of it. This is because that bold timing word is the indication that the controlling player has the option to activate the effect (when all other play restrictions are met).

So by definition, passive effects are never considered triggered effects. A passive effect may "trigger" when its play restrictions are met, but a player has no choice in whether it happens or not. Without that element of a player choosing whether the effect initiates or not, you have not met the game's definition of "triggered effect."

Ambush is the only keyword that has that element of player choice (don't confuse player choice in how the effect resolves - like with Stealth - with the player having a choice in whether or not the effect initiates ) and is thus defined as a triggered effect. It's worth noting that the definition of Ambush contains a bold timing word (Any Phase). But, as stated in the FAQ, keywords cannot be canceled anyway.

Any effect that has the "phase : effect xy" - structure is considered to be a triggered effect. From the faq:

(3.6) Triggered Effects
Any effect that a player chooses to execute is
considered a "triggered effect." Thus any effect
that begins with a "Phase:" or "Response:"
is a triggered effect. Also note that playing
an event card is thus considered a triggered
effect. A "triggered ability" is a triggered effect
printed on a card already in play.

Usually keywords aren´t triggered effects , the only notable exception is "Ambush". But because this turned out to be confusing FFG added the rule that keywords with a point of initiation can´t be cancelled.

(4.14) Keywords
Keyword effects with a point of initiation
(such as ambush) cannot be canceled.
Characters can be saved from the effects of a
keyword like deadly

I thought I remembered(I can't find it) that you(ktom) said that vigilant was a triggered effect, or something that is not obvious?

Egg said:

Nope. I said that Vigilant was NOT a triggered effect. The "non-obvious" part of that discussion was that since a player has options for how Vigilant resolves, including an option for what is essentially a meaningless resolution, people often mistake it for a triggered effect. But choosing an option for how an effect resolves is not the same thing as choosing whether or not the effect initiates (which isn't obvious to many people). No player chooses whether or not Vigilant initiates - it just does (then a player chooses how it ultimately resolves). That makes it a passive, not triggered, effect.

what might have been confusing is that Ktom pointed out that vigilant is a passive may effect (optional) as opposed to a passive must effect (manditory). see Bandit of summer for a pssive must effect.