So I have Marisi, Breaker of the Coil on the battlefield. I cast Ghired, Conclave Exile in my M1. I wait for response. No response. Then I say, "Move to combat". Opponent says, "I will cast (some instant)". I respond, "you can't because I'm in combat". He recants and says, "I cast in response to end of M1".
So my questions: Can opponents instants be cast at the end of a phase? At the start of a phase?
Nothing happens "between" steps or phases (C.R. 500.11). In general, a step or phase where players get priority, including the main phase, ends only if all players pass in a row while the stack is empty (C.R. 500.2, 505.5).
Also, by saying you will move to combat, you are merely proposing a shortcut that any other player can shorten (C.R. 727.2a-b; for sanctioned tournaments, see M.T.R. 4.2). For example, after you say "move to combat" during your first main phase, your opponent can shorten this shortcut by proposing to cast an instant spell during that same main phase; if they do, and no one else shortens or has shortened the shortcut further, the opponent will get to cast that spell and the game will still be in your first main phase (C.R. 727.2a-c, 115.1a; for sanctioned tournaments, see M.T.R. 4.2).
EDIT: Clarification in first paragraph after comment 7 was posted.
EDIT (Dec. 23): Add rule citation.
EDIT (Jul. 9, 2023): Some rules were renumbered in the meantime.
Nothing happens "between" steps or phases. In general, a step or phase, including the main phase, ends only if all players pass while the stack is empty (C.R. 500.2).
Also, by saying you will move to combat, you are merely proposing a shortcut that any other player can shorten. For example, after you say "move to combat" during your main phase, your opponent can shorten it by casting an instant spell during that same main phase. If they do, and assuming this is a two-player game, the instant is cast and the game will still be in your main phase.
So once I cast my last spell for the phase, all players have a chance to respond to the phase ending. So I can say, "Move to Combat". But that would not prevent other players from casting a spell at the end of main 1. They still the opportunity, and I can't circumvent that by just saying, "Move to combat".
So once I cast my last spell for the phase, all players have a chance to respond to the phase ending. So I can say, "Move to Combat". But that would not prevent other players from casting a spell at the end of main 1. They still the opportunity, and I can't circumvent that by just saying, "Move to combat".
You understand correctly. In general, players can't end the main phase unilaterally (C.R. 500.2).
Also note, that since your shortcut was not accepted, you are not bound to keep from playing more stuff in the same step/phase. The game is still in your first main phase, even after your opponent's spell/ability has resolved. So you could then still play a creature for example in the precombat main phase afterwards.
Also note, that since your shortcut was not accepted, you are not bound to keep from playing more stuff in the same step/phase. The game is still in your first main phase, even after your opponent's spell/ability has resolved. So you could then still play a creature for example in the precombat main phase afterwards.
Ok right. So when everyone passes priority, we move on. But if one person plays in Main 1, then it resets and everyone has to pass again to move to the next phase.
All players have to pass priority in succession while the stack is empty for the game to move to the next step/phase, yes. Only if the entirety of that condition is met at the same time will the current step/phase end.
So my questions: Can opponents instants be cast at the end of a phase? At the start of a phase?
Also, by saying you will move to combat, you are merely proposing a shortcut that any other player can shorten (C.R. 727.2a-b; for sanctioned tournaments, see M.T.R. 4.2). For example, after you say "move to combat" during your first main phase, your opponent can shorten this shortcut by proposing to cast an instant spell during that same main phase; if they do, and no one else shortens or has shortened the shortcut further, the opponent will get to cast that spell and the game will still be in your first main phase (C.R. 727.2a-c, 115.1a; for sanctioned tournaments, see M.T.R. 4.2).
See also this thread.
EDIT: Clarification in first paragraph after comment 7 was posted.
EDIT (Dec. 23): Add rule citation.
EDIT (Jul. 9, 2023): Some rules were renumbered in the meantime.
So once I cast my last spell for the phase, all players have a chance to respond to the phase ending. So I can say, "Move to Combat". But that would not prevent other players from casting a spell at the end of main 1. They still the opportunity, and I can't circumvent that by just saying, "Move to combat".
EDIT (Feb. 6): Correctness edit.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
Ok right. So when everyone passes priority, we move on. But if one person plays in Main 1, then it resets and everyone has to pass again to move to the next phase.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)