Skeleton Key 
Artifact — Equipment
$0.27 #8585 0.14 10.5 years
Equipped creature has skulk. (It can't be blocked by creatures with greater power.)
Whenever equipped creature deals combat damage to a player, you may draw a card. If you do, discard a card.
Equip 
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Cards similar to Skeleton Key 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.
Zephyr Boots90%
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"Whenever equipped creature deals combat damage to a player, draw a card, then discard a card."
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"Creatures you control have skulk."
Daring Saboteur80%
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"Whenever this creature deals combat damage to a player, you may draw a card. If you do, discard a card."
Jeskai Elder80%
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"Whenever this creature deals combat damage to a player, you may draw a card. If you do, discard a card."
Assassin Gauntlet79%
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Pip-Boy 300079%
$5.77↑#2708↑0.25↑2.6 years↓
"Equip "
"
Abomination of Gudul76%
$0.06↓#27754↓0.0712.1 years↑
"Whenever this creature deals combat damage to a player, you may draw a card. If you do, discard a card."
Mask of the Schemer76%
$2.51↑#11531↓0.074.5 years↓
"Whenever equipped creature deals combat damage to a player, it connives X, where X is the amount of damage it dealt to that player."
+1 more matching line
Tomebound Lich75%
$0.34↑#13696↓0.057.3 years↓
"Whenever this creature enters or deals combat damage to a player, draw a card, then discard a card."
Looter il-Kor74%
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"Whenever this creature deals damage to an opponent, draw a card, then discard a card."
Wharf Infiltrator72%
$0.33↑#6626↑0.00↓10.2 years
"Whenever this creature deals combat damage to a player, you may draw a card. If you do, discard a card."
+1 more matching line
Izzet Keyrune72%
$0.26↓#15656↓0.00↓14.0 years↑
"Whenever this artifact deals combat damage to a player, you may draw a card. If you do, discard a card."
April, Reporter of the Weird72%
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"Whenever this card deals combat damage to a player, draw that many cards, then discard a card."
Trickster's Talisman72%
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"Equip "
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Bilbo, Luckwearer // Burglar's Plot71%
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"Whenever this card deals combat damage to a player, draw a card, then discard a card."
Surge Mare71%
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"Whenever this creature deals damage to an opponent, you may draw a card. If you do, discard a card."
Thieves' Tools71%
$0.22↓#5953↑0.00↓5.2 years↓
"Equip "
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Jace, Cunning Castaway70%
$10.71↑#11190↓0.31↑9.1 years↓
"+1: Whenever one or more creatures you control deal combat damage to a player this turn, draw a card, then discard a card."