This is my basis for the backup (actually a rewind):

Originally posted by IPG:

A player who makes a play that may or may not be legal depending on whether an uncommunicated trigger has been remembered has not committed an infraction; their play either succeeds, confirming that the trigger has been missed, or is rewound

In this instance Adam has tried to draw and cast the Advantage both of which were illegal given that Norbert has remembered his trigger - but this is not an infraction and is rewound. Had Adam drawn, shuffled his hand about then cast I would declare missed trigger, but in this case speed of draw to cast means missed trigger in my book. This is a little odd as the IPG gives us two different takes on determining a missed trigger. First this one where an action confirms it was forgotten, then that the owner has to take an active part.

Adam in this instance has done more than most players do (declaring Untap, Upkeep, Draw) and even if he had been moving quickly hoping Norbert would miss the trigger this isn't cheating so I'm not investigating on that line. While we might not like such play it doesn't break the rules.

Edited Marc Shotter (July 27, 2015 02:54:19 AM)

The trigger is remembered and would be placed at the bottom of the stack. We wouldn't back up here and we're already past the point where the trigger should have been on the stack. It'll be a bit odd, but Mogis will be sacrificed (presumably) before his trigger will resolve.

There would be no warning for either player (as the triggered ability is not generally detrimental to its controller) with the usual caveat that if this weren't a Knowledge Pool scenario there would definitely be an investigation.

Hello again friends! Let's get down to it!
Norbert has not missed his trigger. He demonstrated awareness of the trigger before taking an active role (such as taking an action or explicitly passing priority). Therefore no penalty is applied and the trigger resolves.

The new bit of the IPG we wanted to highlight here is some clarifying wording on when a trigger is missed by NAP.

Players may not cause triggered abilities controlled by an opponent to be missed by taking game actions or otherwise prematurely advancing the game. During an opponent’s turn, if a trigger’s controller demonstrates awareness of the trigger before they take an active role (such as taking an action or explicitly passing priority), the trigger is remembered.

Thanks for your contributions, check back soon for our next scenario

Originally posted by Meghan Baum:

Therefore no penalty is applied and the trigger resolves.

Given that the IPG is silent on how to resolve the trigger at this point, could you explain what the best way to do so is? I've seen a number of options listed in this thread:

1) Resolve the trigger immediately, without using the stack
2) Put the trigger on top of the stack now
3) Put the trigger on the bottom of the stack now
4) Rewind to the point where the trigger should have occurred

Is there any guidance on which of these approaches is the “most correct” way to handle this trigger?

From the Additional Remedy:
“If the triggered ability specifies a default action associated with a choice made by the controller (usually ”If you don't …“ or ”… unless“), resolve it choosing the default option. … the opponent chooses whether to resolve the ability the next time a player would get priority or when a player would get priority at the start of the next phase.”

Contrast this wording with the remedy for other types of missed triggers: “If the triggered ability isn’t covered by the previous two paragraphs, the opponent chooses whether the triggered ability is added to the stack.”

Nothing in the first paragraph says anything about rewinding or using the stack. So we just resolve it immediately with the default option. Adam takes 2, and play resumes.

Edited Jack Hesse (Aug. 4, 2015 11:19:04 AM)

I think Vincent's question comes from the fact that there was no infraction here, so the Additional Remedy for Missed Trigger is not applicable since there was no Missed Trigger. :)

Even so, I think it makes the most sense to fix the gamestate as if the default option was chosen, with Adam taking 2 and moving on.

Originally posted by Claudio Martín Nieva Scarpatti:

Even so, I think it makes the most sense to fix the gamestate as if the default option was chosen, with Adam taking 2 and moving on.

It's worth noting that the “default action” clause does not apply here. We automatically perform the default action only if it is a "default action associated with a choice made by the controller [of the triggered ability]". In this case, the choice is made not by the controller, but by the opponent; therefore, this clause doesn't apply.

Originally posted by Vincent Roscioli:

It's worth noting that the “default action” clause does not apply here. We automatically perform the default action only if it is a "default action associated with a choice made by the controller [of the triggered ability]". In this case, the choice is made not by the controller, but by the opponent; therefore, this clause doesn't apply.

Well spotted, and completely true. In that case, I think the best option would be to resolve the trigger immediately.