I'm necroing this thread because I'm really confused by this ruling, after trying to make sense of it. I thought I got it, but now I realize I never did.
The bottom line was that when Alice plays Urchin and Bob has a Moat, Alice has to trash Urchin before Bob reveals the Moat.
But: When Alice buys an Embargoed Noble Brigand, she can choose to resolve Noble Brigand before Embargo.
The reasoning is that Noble Brigand ("when you buy this") affects Alice, but Bob's Moat doesn't. If his Moat affected her too, she would get to choose which should be resolved first (Moat's or Urchin's when-play ability).
But why is Noble Brigand different from Moat?
For Moat, Donald said: Getting to decide whether or not to reveal your Moat is "something happening to you." The idea is that it's happening to Bob, not to Alice.
But that's not the trigger. This is the trigger:
Noble Brigand says "when you buy this". -- "You" in this case is Alice.
Moat says "when another player plays an Attack card". -- "Another player" in this case is Alice.
In both cases the trigger is Alice (not Bob) actively doing something.
So what about "deciding whether or not to reveal your Moat". That's part of resolving the ability.
Noble Brigand: "each other player reveals the top 2 cards of his deck..." -- This means Bob.
Moat: "you may reveal this from your hand." -- This means Bob.
In both cases Bob does something as part of the resolution, so it seems that both cards entail "something happening" to Bob.
I can only see these two differences:
1) Moat entails a choice for Bob, Noble Brigand doesn't. But nowhere, in the rulebooks or in this thread, is choice mentioned as a distinguishing factor. (Edit: This turned out to be the answer!)
2) The Moat card belongs to Bob, the Noble Brigand card doesn't. But the Noble Brigand doesn't belong to Alice either, not yet.
What am I missing?