Mystery Key 

Artifact — Equipment
$0.12 #17418 0.00 4.4 years
When equipped creature deals combat damage to a player, sacrifice this Equipment. If you do, draw three cards.
Equip
(
: Attach to target creature you control. Equip only as a sorcery.)
Click a line or tag to filter
Cards similar to Mystery 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.
Impaler Shrike82%
$0.15↑#201770.12↑15.4 years↑
"Whenever this creature deals combat damage to a player, you may sacrifice it. If you do, draw three cards."
Goggles of Night80%
$0.12#11820↑0.064.4 years
"Whenever equipped creature deals combat damage to a player, scry 1, then draw a card."
+1 more matching line
Rogue's Gloves78%
$0.31↑#4162↑0.0612.3 years↑
"Whenever equipped creature deals combat damage to a player, you may draw a card."
+1 more matching line
Robe of the Archmagi77%
$0.42↑#5087↑0.27↑4.4 years
"Whenever equipped creature deals combat damage to a player, you draw that many cards."
Mask of Riddles74%
$0.52↑#7547↑0.27↑17.5 years↑
"Whenever equipped creature deals combat damage to a player, you may draw a card."
+1 more matching line