I strongly disagree that the demon trigger is in the process of being resolved there. AP has interrupted his own shortcut to announce a trigger. NAP has a chance to respond.

Nathaniel, in your opinion what should AP have said to use the shortcut (with his trigger implicitly on the stack by default), and have the trigger resolve when his opponent says OK (so he implicitly passes priority during the beginning of combat step, right?), and without "interrupting his own shortcut“?
Don't you think NAP's ”chance to respond" was when the shortcut was proposed, not after he accepted it without mentionning any action nor explicitly retaining priotiry?

I don't think that the default shortcut works here because of the existence of the trigger. If the shortcut is accepted and neither player calls attention to the trigger, ok. It's been missed and we're now beyond the beginning of combat step.

I do not believe at all that the implicit existence of the trigger and the language used here affords AP the chance to juke NAP into a priority pass with the trigger on the stack, causing him to miss the opportunity to respond to the effect. In essence, there is no way to achieve what you are describing. If either player calls attention to that trigger explicitly before any other actions are taken that would imply we've passed the point where that could happen (i.e. “Go to attacks?” “Ok” *AP taps demon* “Wait I want to activate a Mutavault and sac” (although in this case AP is probably getting a warning for missing his detrimental trigger)), then I'm going to be ruling that we're still in the beginning of combat step.

We allow for players to influence their opponents' decisions via linguistics, but we also have to completely acknowledge that players should have a chance to do things at an appropriate time - the shortcuts in the MTR are designed to facilitate smooth player interaction, not a way to scam your opponent out of a legitimate opportunity to act. Using the default shortcut language is not and cannot implicitly cause the resolution of this triggered ability, in my opinion.

Originally posted by Chris Nowak:

I just wanted to call out an assumption I didn't realize I'd been making (that I only figured out when working through Uncle Scott's first example there), in case others are making it as well.

Thanks, I was making the same assumption ;).
And I think you propousse quite a good example. In this, AP is technically following the rules; he is remebering NAP that he has to make a choice, and he is demostrating awareness of “what the action taken or choice made is before taking any game actions (such as casting a sorcery spell or explicitly moving to the next step or phase) that can be taken only after the triggered ability should have resolved”. And, as per MTR, he is not interrupting any shortcut, cause the shortcut ends when “opponent has priority in the beginning of combat step”. How much can/should we “handwave” (quoting tony) on this?