Farsight Mask 
Artifact
$0.35 #15372 0.44 22.9 years
Whenever a source an opponent controls deals damage to you, if this artifact is untapped, you may draw a card.
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Cards similar to Farsight Mask 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.
Retaliator Griffin76%
$0.33↓#22139↓0.14↓17.3 years↓
"Whenever a source an opponent controls deals damage to you, you may put that many +1/+1 counters on this creature."
Well of Discovery75%
$0.42↑#26810↓0.3826.3 years↑
"At the beginning of your end step, if you control no untapped lands, draw a card."
Howling Mine74%
$5.04↑#716↑0.29↓33.1 years↑
"At the beginning of each player's draw step, if this artifact is untapped, that player draws an additional card."
Awaken the Sky Tyrant72%
$0.29↓#23359↓0.05↓10.8 years↓
"When a source an opponent controls deals damage to you, sacrifice this enchantment. If you do, create a 5/5 red Dragon creature token with flying."
Sphinx's Disciple70%
$0.11↓#23285↓0.07↓12.6 years↓
"Whenever this creature becomes untapped, draw a card."
Thunderstaff70%
$0.27↓#21499↓0.00↓22.6 years
"As long as this artifact is untapped, if a creature would deal combat damage to you, prevent 1 of that damage."
Neurok Commando70%
$0.08↓#18935↓0.15↓15.6 years↓
"Whenever this creature deals combat damage to a player, you may draw a card."
Iymrith, Desert Doom70%
$1.31↑#5337↑0.19↓5.1 years↓
"Whenever this card deals combat damage to a player, draw a card. Then if you have fewer than three cards in hand, draw cards equal to the difference."
Angelheart Vial70%
$0.40↑#175850.22↓16.4 years↓
"Whenever you're dealt damage, you may put that many charge counters on this artifact."