Say a player uses a Vampire Hexmage to remove all the counters from their Dark Depths, then in response there's a long series of events. After the stack clears, Player A forgets their Dark Depths trigger and passes the turn. Player A later remembers their Dark Depths trigger, but it's way outside the time limit for “missed trigger”. What happens?

The main confusion is that Dark Depths has a “when” trigger, meaning that it triggers whenever a certain state is true. As in, if you Stifle a Dark Depths trigger, it won't do anything because Dark Depths will simply trigger again. How does this work with Missed Trigger policy?

Thanks.

As you pointed out, it is constantly triggering due to meeting a game state. The player continues to miss his trigger, so I would do nothing until he realizes his mistake. I would expect his opponent to do the same.

As soon as he realizes it triggers, put it on the stack. The condition is still being met. It's not triggering any less 4 turns later!

The trigger is missed, but since it's not considered generally detrimental (without the trigger, the card wouldn't be played, so it's positive it's there), there are no warnings. A judge doesn't have to intervene or give warnings. If a judge were to interfere (because they are called over), follow the next procedure:

If more than a turn have passed, the rules of the game put the trigger on the stack now, on top of whatever is currently on the stack.

If we're still in the turn cycle, the opponent gets to choose if the trigger goes on the stack now or at the beginning of the next step. If the opponent doesn't put it on the stack, the rules of the games do.
The rules of the game would put the trigger on top of the stack, while the additional remedy of the missed trigger policy put it on the bottom of the stack. Note that the rules of the game do not put the trigger on the stack if the opponent chooses to do so, since the rules for state triggers say a state trigger won't trigger again while it's still on the stack.

Originally posted by Jasper Overman:

If we're still in the turn cycle, the opponent gets to choose if the trigger goes on the stack now or at the beginning of the next step. If the opponent doesn't put it on the stack, the rules of the games do.

If the opponent choses to put the trigger on the stack at the beginning of the next step, don't the game rules put it on the stack anyway? The trigger isn't on the stack yet, so the rules for state triggers don't seem to apply.

Originally posted by Jasper Overman:

If we're still in the turn cycle, the opponent gets to choose if the trigger goes on the stack now or at the beginning of the next step. If the opponent doesn't put it on the stack, the rules of the games do.

As this is not a trigger which has a default action that depends on a choice made by the opponent, and it is not a delayed zone change trigger, the opponent gets to put it on the stack immediately or not at all. They don't have the option to put it on at the beginning of the next step.

Of course that's all moot, even if they don't put the trigger on the stack it's triggering again anyway.

So… Coaching question.

So lets say a player manages to forget this trigger, goes to sac the creature, and the opponent calls for a judge.

The most strict answer is “Yes, that's a missed trigger. It isn't generally detrimental, so no warning. Opponent, do you want to let it happen? No. OK, keep playing”.

Do we just leave it there, and maybe stick around in case the player realizes the trigger goes of again?

Originally posted by Chris Nowak:

So… Coaching question.

So lets say a player manages to forget this trigger, goes to sac the creature, and the opponent calls for a judge.

The most strict answer is “Yes, that's a missed trigger. It isn't generally detrimental, so no warning. Opponent, do you want to let it happen? No. OK, keep playing”.

Do we just leave it there, and maybe stick around in case the player realizes the trigger goes of again?

I assume so, but I would be extremely surprised if the player didn't ask something along the lines of “Wait, so now I'll never get my token?” or something like that. To which you would normally answer that the condition for the state trigger is met.