Sunken Palace
Land — Cave
This land enters tapped.
{T}: Add {U}.
{1}{U}, {T}, Exile seven cards from your graveyard: Add {U}. When you spend this mana to cast a spell or activate an ability, copy that spell or ability. You may choose new targets for the copy. (Mana abilities can't be copied.)
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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.
Oaken Siren 98%
$0.30#10524
"{T}: Add {U}. Spend this mana only to cast an artifact spell or activate an ability of an artifact source."
Unblinking Observer 98%
$0.16#18594
"{T}: Add {U}. Spend this mana only to pay a disturb cost or cast an instant or sorcery spell."
Karfell Harbinger 97%
$0.20#14919
"{T}: Add {U}. Spend this mana only to foretell a card from your hand or cast an instant or sorcery spell."