Several cards include effects of the form "For each [item], A unless B", where a player chooses to do B multiple times. They include the following cards:
May involve multiple players:
Cleansing: "For each land, destroy that land unless any player pays 1 life." Cut the Tethers: "For each Spirit, return it to its owner's hand unless that player pays 3." Giant Albatross: "...for each creature that dealt damage to Giant Albatross this turn, destroy that creature unless its controller pays 2 life". Heroism: "For each attacking red creature, prevent ... unless its controller pays 2R." Killing Wave: "For each creature, its controller sacrifices it unless they pay X life." Lim-Dûl's Hex: "... for each player, Lim-Dûl's Hex deals 1 damage to that player unless they pay B or 3." Stench of Evil: "For each land destroyed this way, Stench of Evil deals 1 damage to that land's controller unless they pay 2."
Involves only one player:
Delaying Shield: "For each delay counter removed this way, you lose 1 life unless you pay 1W." Moonlight Bargain: "For each card, put that card into your graveyard unless you pay 2 life." Oath of Lim-Dûl: "... for each 1 life you lost, sacrifice a permanent other than Oath of Lim-Dûl unless you discard a card." Read the Runes: "For each card drawn this way, discard a card unless you sacrifice a permanent." Sirocco: "For each blue instant card revealed this way, that player discards that card unless they pay 4 life."
In addition, Sylvan Library is a similar case: "For each of those cards, pay 4 life or put the card on top of your library". (For the sake of discussion, assume Sylvan Library reads here "For each of those cards, put ... unless you pay 4 life.")
Note that:
All these cards except the current version of Sylvan Library are governed by C.R. 118.12a so that, for example, Heroism's effect means "For each attacking red creature, its controller may pay ... If that player doesn't, prevent ...", so that performing B is a cost (C.R. 118.12) and is therefore subject to the rules on costs (C.R. 118).
In general, "for each" actions happen simultaneously (under C.R. 608.2c, when following an ability's instructions, a player "appl[ies] the rules of English to [its] text") — a relevant example is cumulative upkeep (C.R. 702.24a).
Do official rulings exist that answer any or all of the following questions?
For all these cards, can a player—
choose a number X or less, where X is the lesser of—
— the number of items in which that player is involved, and
— the number of times that player can perform B at once (see also C.R. 117.12, 117.3), then
perform B the chosen number of times, then
perform A as often as possible but no more than Y times, where Y is the balance (C.R. 609.3)?
In this case, do performing B and performing A happen simultaneously?
Or is the player limited to choosing between—
performing B, Z times, where Z is the number of items in which that player is involved, and then only if that player can perform B that many times (see also C.R. 118.12), and
performing A as often as possible but no more than Z times?
For at least Killing Wave, and perhaps for other cards that involve multiple players, the effect is governed in part by C.R. 101.4, which specifies the procedure for making choices if multiple players have to make them at the same time. However, C.R. 101.4 doesn't apply to Read the Runes, Oath of Lim-Dûl, the case of Heroism where all attacking creatures are controlled by one player, the case of Cut the Tethers where all Spirits on the battlefield are owned and controlled by only one player, or any other situation where multiple players aren't involved. And it seems to me that the comprehensive rules don't properly cover simultaneity of actions for effects of the form "For each ..., A unless B" where multiple players aren't involved (correct me if I'm wrong).
Moreover, what if action B involves paying mana, as is the case for Cut the Tethers and Delaying Shield? For such cards, which combinations of the following actions happen simultaneously?
Activating mana abilities (C.R. 605.3a).
Performing B as often as allowed and possible.
Performing A as often as allowed and possible.
Does the answer change, if multiple players are involved as opposed to if only one player is involved?
Where multiple players are involved, Lim-Dûl's Hex includes an additional complication that players can choose how to pay. Is—
the choice of how to pay, and/or
the choice of a number X or less, where X is defined above,
made as players activate mana abilities or as players pay mana (assuming the answer is that both are not simultaneous)?
EDIT (Jan. 2, 2023): Edited, including to conform to Oracle text and rule updates in the meantime.
"Do A unless B" is merely sugar for "Maybe B. If not, A." So I am confident there is no restriction on the permutations allowed between choosing A and/or B for each concerned object. But the order doesn't matter because of, as you note, CR 608.2c. For example, Killing Wave resolves with X = 4. Your opponent sacrifices some creatures and pays N*4 life, as do you, all at once (although one player can see the choices of the other first).
Mana payments are the only irregular element. 608.2f says you get to activate mana abilities "before taking that action" - the action of paying the mana. So the event timeline would be 1) first you're allowed to activate mana abilities, then 2) you decide and announce how many As or Bs you're going to choose, then 3) you actually do the As and Bs.
I'm sorry, but I can't see what the fuss is about, and maybe missed the depth of your question.
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As I just found out, at least for Read the Runes, an official ruling exists that suggests that discarding multiple cards and sacrificing multiple permanents with that particular spell are each simultaneousthat is written in the following form: "You draw ... then sacrifice ... then discard the required number of card(s)".
However, since that ruling probably existed ever since Gatherer was started, it could not have anticipated the advent of cards such as Rielle, the Everwise in Ikoria: Lair of Behemoths that care whether one or more cards were discarded at the same time. Moreover:
This ruling does not comprehensively clarify how effects of the form "For each..., A unless B" work, especially because there is currently no similar ruling for Oath of Lim-Dûl (which likewise has the form "...for each ..., A unless B"), Moonlight Bargain, Heroism, Cut the Tethers, Sirocco, or Delaying Shield.
It's still apparently the case that "C.R. 101.4 doesn't apply to Read the Runes, Oath of Lim-Dûl, the case of Heroism where all attacking creatures are controlled by one player, the case of Cut the Tethers where all Spirits on the battlefield are owned by only one player, or any other situation where multiple players aren't involved", for the reasons given in comment 1.
With the release of Commander Legends, a new rule, which has taken on the existing rule number C.R. 608.2f, was added to the comprehensive rules to cover "actions taken on multiple players and/or objects", especially actions of the form "For each ..., A unless B". Since "A unless B" "can't be processed simultaneously, it's instead processed considering each affected player or object individually", as further described in new C.R. 608.2f.
Thus, for example, in the case of Oath of Lim-Dûl, the controller of that spell does the following for each 1 life referred to by its ability (see also C.R. 109.5):
They choose a permanent other than Oath of Lim-Dûl they control.
They then choose whether to discard a card, and the player sacrifices that permanent if they don't (C.R. 118.12a).
Several cards include effects of the form "For each [item], A unless B", where a player chooses to do B multiple times. They include the following cards:
May involve multiple players:
Cleansing: "For each land, destroy that land unless any player pays 1 life."
Cut the Tethers: "For each Spirit, return it to its owner's hand unless that player pays 3."
Giant Albatross: "...for each creature that dealt damage to Giant Albatross this turn, destroy that creature unless its controller pays 2 life".
Heroism: "For each attacking red creature, prevent ... unless its controller pays 2R."
Killing Wave: "For each creature, its controller sacrifices it unless they pay X life."
Lim-Dûl's Hex: "... for each player, Lim-Dûl's Hex deals 1 damage to that player unless they pay B or 3."
Stench of Evil: "For each land destroyed this way, Stench of Evil deals 1 damage to that land's controller unless they pay 2."
Involves only one player:
Delaying Shield: "For each delay counter removed this way, you lose 1 life unless you pay 1W."
Moonlight Bargain: "For each card, put that card into your graveyard unless you pay 2 life."
Oath of Lim-Dûl: "... for each 1 life you lost, sacrifice a permanent other than Oath of Lim-Dûl unless you discard a card."
Read the Runes: "For each card drawn this way, discard a card unless you sacrifice a permanent."
Sirocco: "For each blue instant card revealed this way, that player discards that card unless they pay 4 life."
In addition, Sylvan Library is a similar case: "For each of those cards, pay 4 life or put the card on top of your library". (For the sake of discussion, assume Sylvan Library reads here "For each of those cards, put ... unless you pay 4 life.")
Note that:
Do official rulings exist that answer any or all of the following questions?
For all these cards, can a player—
— the number of times that player can perform B at once (see also C.R. 117.12, 117.3), then
In this case, do performing B and performing A happen simultaneously?
Or is the player limited to choosing between—
For at least Killing Wave, and perhaps for other cards that involve multiple players, the effect is governed in part by C.R. 101.4, which specifies the procedure for making choices if multiple players have to make them at the same time. However, C.R. 101.4 doesn't apply to Read the Runes, Oath of Lim-Dûl, the case of Heroism where all attacking creatures are controlled by one player, the case of Cut the Tethers where all Spirits on the battlefield are owned and controlled by only one player, or any other situation where multiple players aren't involved. And it seems to me that the comprehensive rules don't properly cover simultaneity of actions for effects of the form "For each ..., A unless B" where multiple players aren't involved (correct me if I'm wrong).
Moreover, what if action B involves paying mana, as is the case for Cut the Tethers and Delaying Shield? For such cards, which combinations of the following actions happen simultaneously?
Does the answer change, if multiple players are involved as opposed to if only one player is involved?
Where multiple players are involved, Lim-Dûl's Hex includes an additional complication that players can choose how to pay. Is—
EDIT (Jan. 2, 2023): Edited, including to conform to Oracle text and rule updates in the meantime.
Mana payments are the only irregular element. 608.2f says you get to activate mana abilities "before taking that action" - the action of paying the mana. So the event timeline would be 1) first you're allowed to activate mana abilities, then 2) you decide and announce how many As or Bs you're going to choose, then 3) you actually do the As and Bs.
I'm sorry, but I can't see what the fuss is about, and maybe missed the depth of your question.
Awesome avatar provided by Krashbot @ [Epic Graphics].
that suggests that discarding multiple cards and sacrificing multiple permanents with that particular spell are each simultaneousthat is written in the following form: "You draw ... then sacrifice ... then discard the required number of card(s)".However, since that ruling probably existed ever since Gatherer was started, it could not have anticipated the advent of cards such as Rielle, the Everwise in Ikoria: Lair of Behemoths that care whether one or more cards were discarded at the same time. Moreover:
, especially because there is currently no similar ruling for Oath of Lim-Dûl (which likewise has the form "...for each ..., A unless B"), Moonlight Bargain, Heroism, Cut the Tethers, Sirocco, or Delaying Shield.It's still apparently the case that "C.R. 101.4 doesn't apply to Read the Runes, Oath of Lim-Dûl, the case of Heroism where all attacking creatures are controlled by one player, the case of Cut the Tethers where all Spirits on the battlefield are owned by only one player, or any other situation where multiple players aren't involved", for the reasons given in comment 1.EDIT (Nov. 28, 2020): See comment 4.
Thus, for example, in the case of Oath of Lim-Dûl, the controller of that spell does the following for each 1 life referred to by its ability (see also C.R. 109.5):