Bone Mask {4}
Artifact
{2}, {T}: The next time a source of your choice would deal damage to you this turn, prevent that damage. Exile cards from the top of your library equal to the damage prevented this way.
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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.
Pentagram of the Ages 96%
#27340
"{4}, {T}: The next time a source of your choice would deal damage to you this turn, prevent that damage."