If a player goes to "combat", and then activates an ability, what is the game state?

Question

My question is not a duplicate of When should I activate Man Lands and Keyrunes in order to attack with them?, although anyone answering this question would need to understand at least that much in order to understand this one. That question only explains when a player would need to activate. It doesn't cover shortcuts or illegal actions, which is what my question is primarily about.

Does activating an ability when you have already decided to move to the declare attackers step imply that you are declaring zero attackers?

Anthony: Combat?
Noah: Sure.
Anthony: Animate Mutavault?
Noah: Sure.
Anthony: Declare attackers?
Noah: Hang on. You're already in the declare attackers phase, right? I thought you animated Mutavault after you decided to declare no attackers.

Anthony offers the shortcut "Combat?". According to the Tournament Rules, that means he is offering to pass priority until Noah has priority in the Beginning of Combat step.

A statement such as "I'm ready for combat" or "Declare attackers?" offers to keep passing priority until an opponent has priority in the beginning of combat step. Opponents are assumed to be acting then unless they specify otherwise.

Noah responds with "Sure." I believe this means that Noah is passing priority back to Anthony (don't get too hung up on this - it isn't the focus of the question). That means the game moves to the Declare Attackers step.

Anthony activates Mutavault, which is an action that could, if it is legal, only be taken after declaring attackers. Now the game state is potentially ambiguous.

508.1. First, the active player declares attackers. This turn-based action doesn’t use the stack
...
508.3. Third, the active player gets priority

Assume the tournament level is Competitive REL, and that if a judge is needed, one will be called. What is the resulting game state? I believe the resulting game state would be one of the following, but I am not sure which is correct (if either):

• The game is in the Declare Attackers phase, and Anthony does not have the opportunity to declare attackers.
• Activating Mutavault was an illegal action because Anthony didn't have priority. That action is reversed. The game is in the Declare Attackers phase, and Anthony still has the opportunity to declare attackers.

Answer 1

As of the release of Amonkhet, the "Go to combat" tournament shortcut changed, and it now unambiguously supports Anthony's interpretation of the sequence of events. The game is in the beginning of combat step and Mutavault's ability is on the stack. Noah has priority.

The current wording of that shortcut is

If the active player passes priority with an empty stack during their first main phase, the non-active player is assumed to be acting in beginning of combat unless they are affecting whether a beginning of combat ability triggers. However, if the non-active player takes no action, the active player has priority at the beginning of combat. Beginning of combat triggered abilities (even ones that target) may be announced after any non-active player action has resolved.

The Amonkhet policy changes announcement describes the practical impact of the change to this shortcut:

What this does, in a bunch of words, is set the default case so that the active player moving to combat (usually) means that the non-active player is acting in beginning of combat, but the active player’s role there only happens after that. They haven’t missed triggers, and they can still crew. But, by offering to pass priority into combat, they can no longer claim to be in main phase for non-instant spells afterwards unless the non-active player took an action to prevent the trigger.

In the situation in question, activating Mutavault serves the same purpose as the ability to crew that they mention: it turns a non-creature object into a creature in preparation for attacking with it.

In addition, that same blog has a post that takes a more detailed look at the change, and it discusses a scenario that involves actions like those described in the question:

The Cryptic Command Problem

It’s not a problem with the shortcut, per se, but it’s a protection for the non-active player that’s been removed. There are various permutations of the “Phantom Priority Pass”, but here’s a simple one:

The active player has a two Bears and a Mutavault. The non-active player is at 5 life, but active player is worried about a Cryptic Command.

The active player wants to try to get a read on if the coast is clear. So, they say “Combat” in an attempt to imply that they’re ready to declare attackers. If the non-active plays the Cryptic, you activate the Mutavault and get in for 2. If they don’t, unless they’re a very precise player, it’s a strong sign that they may not have it and you should activate the Mutavault and go for it. The old shortcut precluded that baiting.

Of course, the correct time to play the Command if you have it is after the second priority pass (or interrupting the declaration). But now you need to be more careful if you’re the non-active player to not accidentally tip your hand.

The "if they don't [play a Cryptic Command]" scenario plays out exactly like the one in the question: the active player announces that they are moving to Combat, the non-active player takes no action, then the active player activates Mutavault and attacks with it.

Answer 2

Anthony is confused by what the shortcut does. A judge will rewind the game to the point of confusion: Anthony attempting to activate Mutavualt when he is meant to be declaring attackers. The land he used to activate Mutavualt will be untapped and he can proceed with declaring attackers.

It is not Out-Of-Order-Sequencing because he has gained substantial information about what his opponent intends to do during the Beginning of Combat Step (nothing).

The judge should mention that the way to do what Anthony wanted to do was instead of saying "Combat?" was to say "Activate my Mutavualt at the Beginning of Combat?"

Aside: The minor advantage that Anthony is trying to gain: Passing priority in his mainphase without letting his opponent know that he's going to attack with Mutavualt; is such a small advantage that it really isn't worth attempting. The chances of messing it up and having it back fire is much more significant than the strategic advantage attempting to be gained.

Answer 3

Root Cause

The root cause of the problem is the confusion between the short cut offered by Anthony and the shortcut accepted by Noah.

Anthony's intention is to end his 1st Main Phase and transition into the Beginning of Combat. Noah's interpretation is that Anthony wants to pass priority until the end of the Beginning of Combat Phase and transition towards Declare Attackers.

From the April 2017 change to the Magic Tournament Rules, this is the now expected shortcut when moving from the first main phase into the Combat phase.

If the active player passes priority with an empty stack during their first main phase, the non-active player is assumed to be acting in beginning of combat unless they are affecting whether a beginning of combat ability triggers. However, if the non-active player takes no action, the active player has priority at the beginning of combat. Beginning of combat triggered abilities (even ones that target) may be announced after any non-active player action has resolved

When Noah says Sure, Anthony assumes his short cut has been accepted, and takes allowed actions during the Beginning of Combat phase, making Mutavult a creature. Presumably, this is prepatory to declare Mutavult as an attacker during Declare Attackers. Noah states his complaint, possibly citing the implication provided by his short cut per the Tournament Rules. Anthony clarifies what his intentions were by offering his shortcut.

Judgment

If the Judge is called, because the disagreement over the current phase can't be resolved by the players, the Judge should tell Noah that Anthony's interpretation is correct.

Commentary

This is why I am rather pedantic about explicitly declaring the phases I am in during my turn, in order to avoid the associated confusion.