Sleeper Dart 
Artifact
When this artifact enters, draw a card.
{T}, Sacrifice this artifact: Target creature doesn't untap during its controller's next untap step.
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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.
Delif's Cone 80%
$0.34#13612
"{T}, Sacrifice this artifact: This turn, when target creature you control attacks and isn't blocked, you may gain life equal to its power. If you do, it assigns no combat damage this turn."
Moon Girl and Devil Dinosaur 85%
$0.28#22672
"Whenever an artifact you control enters, draw a card. This ability triggers only once each turn."