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Grip of Amnesia allow you to choose to exile all cards from your graveyard even if it has no cards in it, but To the Slaughter does not allow you to choose to sacrifice a card type that you do not control. Why?
Accepted Answer
To "sacrifice a creature or planeswalker" means to sacrifice, to the extent possible, a permanent from the set of creatures and/or planeswalkers controlled by the player in question (C.R. 101.3, 701.16a; see also C.R. 609.3). It doesn't mean to choose creature or planeswalker then sacrifice a permanent of the chosen type. (Compare To the Slaughter with World Queller or Rite of Ruin.)
To "sacrifice a creature and a planeswalker" means to sacrifice two permanents, one of which is a planeswalker and the other a creature, or if both a creature and a planeswalker can't be sacrificed this way, to sacrifice a creature or planeswalker, to the extent possible (C.R. 101.3; see also C.R. 609.3). It doesn't mean to choose both a creature and a planeswalker the player in question controls, and sacrifice both only if it was possible to choose both.
Note that To the Slaughter's effect isn't optional; it must be done if possible. On the other hand, Grip of Amnesia means, in relevant part, "Target spell's controller may exile all cards from their graveyard. If they don't, counter that spell" (C.R. 118.12a, 108.1). Thus, choosing to exile all cards from the graveyard in question is optional. Moreover, the spell's controller can choose to do so even if they have no cards in their graveyard, since performing an action on "all" of something isn't impossible merely because there is none of that something (review C.R. 608.2d). In the same vein, a cost of "Sacrifice all creatures you control" (such as found in Soulblast) can be paid if "you control" no creatures (see also C.R. 118.5 for a similar case).
Go to full postTo "sacrifice a creature and a planeswalker" means to sacrifice two permanents, one of which is a planeswalker and the other a creature, or if both a creature and a planeswalker can't be sacrificed this way, to sacrifice a creature or planeswalker, to the extent possible (C.R. 101.3; see also C.R. 609.3). It doesn't mean to choose both a creature and a planeswalker the player in question controls, and sacrifice both only if it was possible to choose both.
Note that To the Slaughter's effect isn't optional; it must be done if possible. On the other hand, Grip of Amnesia means, in relevant part, "Target spell's controller may exile all cards from their graveyard. If they don't, counter that spell" (C.R. 118.12a, 108.1). Thus, choosing to exile all cards from the graveyard in question is optional. Moreover, the spell's controller can choose to do so even if they have no cards in their graveyard, since performing an action on "all" of something isn't impossible merely because there is none of that something (review C.R. 608.2d). In the same vein, a cost of "Sacrifice all creatures you control" (such as found in Soulblast) can be paid if "you control" no creatures (see also C.R. 118.5 for a similar case).
“Comboing in Commander is like dunking on a seven foot hoop.” – Dana Roach
“Making a deck that other people want to play against – that’s Commander.” – Gavin Duggan
"I want my brain to win games, not my cards." – Sheldon Menery
“Making a deck that other people want to play against – that’s Commander.” – Gavin Duggan
"I want my brain to win games, not my cards." – Sheldon Menery
To "sacrifice a creature or planeswalker" means to sacrifice, to the extent possible, a permanent from the set of creatures and/or planeswalkers controlled by the player in question (C.R. 101.3, 701.16a; see also C.R. 609.3). It doesn't mean to choose creature or planeswalker then sacrifice a permanent of the chosen type. (Compare To the Slaughter with World Queller or Rite of Ruin.)
To "sacrifice a creature and a planeswalker" means to sacrifice two permanents, one of which is a planeswalker and the other a creature, or if both a creature and a planeswalker can't be sacrificed this way, to sacrifice a creature or planeswalker, to the extent possible (C.R. 101.3; see also C.R. 609.3). It doesn't mean to choose both a creature and a planeswalker the player in question controls, and sacrifice both only if it was possible to choose both.
Note that To the Slaughter's effect isn't optional; it must be done if possible. On the other hand, Grip of Amnesia means, in relevant part, "Target spell's controller may exile all cards from their graveyard. If they don't, counter that spell" (C.R. 118.12a, 108.1). Thus, choosing to exile all cards from the graveyard in question is optional. Moreover, the spell's controller can choose to do so even if they have no cards in their graveyard, since performing an action on "all" of something isn't impossible merely because there is none of that something (review C.R. 608.2d). In the same vein, a cost of "Sacrifice all creatures you control" (such as found in Soulblast) can be paid if "you control" no creatures (see also C.R. 118.5 for a similar case).
To "sacrifice a creature and a planeswalker" means to sacrifice two permanents, one of which is a planeswalker and the other a creature, or if both a creature and a planeswalker can't be sacrificed this way, to sacrifice a creature or planeswalker, to the extent possible (C.R. 101.3; see also C.R. 609.3). It doesn't mean to choose both a creature and a planeswalker the player in question controls, and sacrifice both only if it was possible to choose both.
Note that To the Slaughter's effect isn't optional; it must be done if possible. On the other hand, Grip of Amnesia means, in relevant part, "Target spell's controller may exile all cards from their graveyard. If they don't, counter that spell" (C.R. 118.12a, 108.1). Thus, choosing to exile all cards from the graveyard in question is optional. Moreover, the spell's controller can choose to do so even if they have no cards in their graveyard, since performing an action on "all" of something isn't impossible merely because there is none of that something (review C.R. 608.2d). In the same vein, a cost of "Sacrifice all creatures you control" (such as found in Soulblast) can be paid if "you control" no creatures (see also C.R. 118.5 for a similar case).
