I play Martyr's Cause in my Saffi Eriksdotter Commander deck as a free sacrifice outlet. I noticed today that the Oracle text of this card differs from what the card says.
Sacrifice a creature: The next time a source of your choice would deal damage to any target this turn, prevent that damage.
1. Does this ability target? If not, why does it say "target?"
2. Can this prevent damage from a source that does not target? Can I sacrifice a creature to prevent all damage that would be dealt by Blasphemous Act even though Act does not "deal damage to any target?"
1. Martyr's Cause's ability requires a target because its Oracle text identifies a target with the phrase "any target" (C.R. 115.4, 115.1c, 108.1). (Here, "any target" refers to the creature, player, or planeswalker that "a source of your choice" would deal damage to [C.R. 115.4].) Use the Oracle text of a card to determine that card's wording (C.R. 108.1).
2. A spell on the stack can be chosen as the source for Martyr's Cause's ability, even if that spell doesn't require targets and even if it isn't "capable of dealing damage" (C.R. 609.7a).
So I cannot prevent damage that would be dealt TO a creature with shroud? Because that is a change from the written functionality of the card.
By Martyr's Cause's Oracle text and the rules, a permanent or player with shroud can't be the target of Martyr's Cause's ability (C.R. 115.4, 115.1c, 108.1, 702.18a). This is indeed a functional change, just as it's a functional change that that ability can now target a planeswalker, and not necessarily a creature or player, since Dominaria (C.R. 115.4, 108.1). Compare Martyr's Cause with Reflect Damage and see also this thread.
1. Does this ability target? If not, why does it say "target?"
2. Can this prevent damage from a source that does not target? Can I sacrifice a creature to prevent all damage that would be dealt by Blasphemous Act even though Act does not "deal damage to any target?"
2. A spell on the stack can be chosen as the source for Martyr's Cause's ability, even if that spell doesn't require targets and even if it isn't "capable of dealing damage" (C.R. 609.7a).