Adriana's Valor
Conspiracy
Hidden agenda (Start the game with this conspiracy face down in the command zone and secretly choose a card name. You may turn this conspiracy face up any time and reveal that name.)
Whenever a creature you control with the chosen name attacks, you may pay {W}. If you do, that creature gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)
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Cards that do something similar expected a card that isn't here?
Reports become test cases the matcher is graded against before an update ships. Delvefall isn't a chatbot guessing, it compares the printed rules text of every card with plain math, and examples like yours decide which differences should count.
Militia's Pride 89%
$6.66#16726
"Whenever a nontoken creature you control attacks, you may pay {W}. If you do, create a 1/1 white Kithkin Soldier creature token that's tapped and attacking."
Pitfall Trap 86%
$0.19#26280
"If exactly one creature is attacking, you may pay {W} rather than pay this spell's mana cost."
Order of the Golden Cricket 81%
$0.11#26150
"Whenever this creature attacks, you may pay {W}. If you do, it gains flying until end of turn."
Elenda and Azor 80%
$0.49#7376
"Whenever this card attacks, you may pay {X}{W}{U}{B}. If you do, draw X cards."