Originally posted by Eli Meyer:

because N doesn't know for a fact that his block is illegal … his actions don't meet the requirements for USC: Cheating?

Correct. He wasn't breaking a rule, he was either hoping A had missed the trigger (that's allowed) or he himself missed the trigger.

d:^D

Originally posted by Scott Marshall:

Correct. He wasn't breaking a rule, he was either hoping A had missed the trigger (that's allowed) or he himself missed the trigger.

Did you mean to say that he wasn't certain he was breaking a rule? He had to have broken a rule at some point, otherwise we couldn't give him a GRV.

Nope, I meant to say what I said.

Originally posted by Scott Marshall:

Nope, I meant to say what I said.

Okay, I'm super confused now :) Help?

Originally posted by Scott Marshall:

We have not said that it can be OK to assume a trigger was missed - and that's what N does here, by declaring a block that can't be legal unless a poor assumption ends up being correct.

The IPG explicitly says that this is OK:

“* A triggered ability that changes the rules of the game: The controller must acknowledge the trigger or prevent an opponent from taking any resulting illegal action.”

Annotated IPG says about this:
“These are triggered abilities that first matter at the point at which an opponent would first take what would otherwise be an illegal action. In order to avoid missing these triggers, the controller of these abilities must announce the trigger at the correct time and/or actively prevent an opponent from taking an action that wouldn’t be possible had the triggered ability resolved.”

The controller of the prowess trigger must prevent the opponent from blocking with Zurgo, or the trigger is considered missed. The Zurgo player is completely allowed to attempt to block with Zurgo, and it's up to the opponent to stop him. At least this is how I would read the IPG and it doesn't appear to leave much room for interpretation.

Originally posted by Mats Törnros:

Scott Marshall
We have not said that it can be OK to assume a trigger was missed - and that's what N does here, by declaring a block that can't be legal unless a poor assumption ends up being correct.

The controller of the prowess trigger must prevent the opponent from blocking with Zurgo, or the trigger is considered missed. The Zurgo player is completely allowed to attempt to block with Zurgo, and it's up to the opponent to stop him. At least this is how I would read the IPG and it doesn't appear to leave much room for interpretation.

Prowess, and similar triggers that change power and toughness, do not change the rules of the game. The effect of this trigger changes the characteristics of the permanent, which is a completely different concept. Zurgo's ability created a blocking restriction, which affects the rules of a game, but that's a static ability. Not a triggered ability.

An example of a triggered ability that changes the rules of the game would be the last ability of Hero of Oxid Ridge. See also CR 611.2c.

Welp, there's a number of valid concerns expressed in here, and this is now a discussion topic among HL judges; I'll re-open this once there's some consensus.

d:^D

OK, my initial position has been overturned; by putting the Bolster counter on Shu Yun, Adamaro has missed the Prowess trigger - even though he does demonstrate awareness later, at the point where it would *usually* be required (and acceptable), in this case he needs to demonstrate awareness at that point.

In our L4+ discussions, Toby summed up the underlying philosophy quite well:

Originally posted by Toby:

Missed Triggers are defined in terms of *demonstrating* awareness of the trigger at or before the first relevant point, and the rules to do that are concretely defined. That allows the opponent to proceed with a level of certainty (“it's not missed until something happens that shows you it is”). Introducing the idea that there's still a possible timeline where we have a non-missed trigger+GRV is problematic there, and we'd need to shift to rules based on whether the judge believes the player was actually aware of the trigger, rather than demonstrated that awareness.

Jared also added a valuable perspective:

Jared
A GRV is a violation of the game rules and an opponent who is paying attention should be able to catch it and call attention to it. In this case, the opponent has no such ability to catch the error because there was no indication give that the Prowess trigger resolved. In the case of a particularly complex combat, what if you are unwilling to back up and fix the error? In most cases the simple answer of, “if you had caught the error sooner” is perfectly relevant, but in this case, there was nothing to catch until damage assignment, and the opponent was operating under a very straightforward interpretation of what happened.

d:^D