Donatello's Technique {2}{U}
Sorcery
Sneak {U} (You may cast this spell for {U} if you also return an unblocked attacker you control to hand during the declare blockers step.)
Draw two cards.
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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.
Ertai's Scorn 81%
$0.32#9139
"This spell costs {U} less to cast if an opponent cast two or more spells this turn."