NAP Controls a Grizzly Bears.
AP activated his Angrath, the Flame-Chained second ability targeting the bear.
Then AP missed the delay trigger of Angrath's ability and return the bear back to NAP and pass the turn.
Now they notice the issue on NAP's upkeep.
Then what will happen?

My thinking:
According to IPG, the missing of delay trigger ability from Angrath's second ability should be added back to stack and resolve at upkeep or beginning of draw step depending on the choice of NAP.
However, because the Angrath's delay trigger ability is controlled by AP and now the bear is controlled by NAP, so resolving the delay trigger cannot let AP sacrifice NAP's bear.
And nothing will happen.

Is this IPG trully wants in this situation?

More thinking:
If NAP controls a 4 covered mana cost creature instead of a bear, and after AP gained control of the creature , he let it became a copy of a Grizzly Bear until end of turn, then missed the delay trigger.
Since in NAP's upkeep, the creature is 4 covered mana cost, so resolving the delay trigger cannot sacrifice it.

Thanks for your thoughts:)

Originally posted by Chengji Wang:

NAP Controls a Grizzly Bears.
AP activated his Angrath, the Flame-Chained second ability targeting the bear.
Then AP missed the delay trigger of Angrath's ability and return the bear back to NAP and pass the turn.
Now they notice the issue on NAP's upkeep.
Then what will happen?

What if players don't notice, and we do? Should we intervene?
Is the sacrifice ability generally detrimental, as all sacrifice abilities are, or is this a special case?

For reference: https://blogs.magicjudges.org/rules/mtg/standard-detrimental/

I'll add this much, for now: the trigger is not detrimental to its controller.

d:^D

Originally posted by Chengji Wang:

My thinking:
According to IPG, the missing of delay trigger ability from Angrath's second ability should be added back to stack and resolve at upkeep or beginning of draw step depending on the choice of NAP.
However, because the Angrath's delay trigger ability is controlled by AP and now the bear is controlled by NAP, so resolving the delay trigger cannot let AP sacrifice NAP's bear.
And nothing will happen.

Is this IPG trully wants in this situation?

Chengji, you are interpreting the IPG correctly.

And, yes, the guiding philosophy of Missed Triggers that gives the opponent some control over the remedy for missed triggers, is served quite well by the outcome you described - after all, AP had an opportunity to get rid of that pesky Bear, and they missed their chance by missing the trigger.

d:^D

Scott, can you expand on why this trigger isn't considered detrimental? I was under the impression that we didn't take into account separate factors that might change the player's opinion towards the trigger, such as the existence of a control-changing effect that may end later on.

Originally posted by Isaac King:

can you expand on why this trigger isn't considered detrimental?

Sacrificing your opponent's creature is not detrimental. Forgetting to return it would be - but I'm pretty sure the opponent's going to remind you of that one!

d:^D