Oona's Blackguard 
Creature — Faerie Rogue
$0.36 #5805 0.39 18.7 years
Flying
Each other Rogue creature you control enters with an additional +1/+1 counter on it.
Whenever a creature you control with a +1/+1 counter on it deals combat damage to a player, that player discards a card.
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Cards similar to Oona's Blackguard 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.
Larceny88%
$0.29↓#16980↓0.91↑27.0 years↑
"Whenever a creature you control deals combat damage to a player, that player discards a card."
Silent Specter88%
$0.51↑#23400↓0.3724.1 years↑
"Whenever this creature deals combat damage to a player, that player discards two cards."
+1 more matching line
Headhunter88%
$0.30↓#26514↓0.28↓24.0 years↑
"Whenever this creature deals combat damage to a player, that player discards a card."
Blazing Specter86%
$0.68↑#21029↓0.4426.0 years↑
"Whenever this creature deals combat damage to a player, that player discards a card."
Riptide Pilferer84%
$0.13↓#23856↓0.21↓19.7 years
"Whenever this creature deals combat damage to a player, that player discards a card."
Needle Specter84%
$1.12↑#18077↓0.56↑18.2 years
"Whenever this creature deals combat damage to a player, that player discards that many cards."
Specter's Shroud83%
$0.33↓#21306↓0.29↓22.7 years↑
"Whenever equipped creature deals combat damage to a player, that player discards a card."
Orzhov Racketeers82%
$0.05↓#25849↓0.07↓7.7 years↓
"Whenever this creature deals combat damage to a player, that player discards a card."
Cabal Slaver82%
$0.22↓#25821↓0.4424.0 years↑
"Whenever a Goblin deals combat damage to a player, that player discards a card."
Sedraxis Specter82%
$0.10↓#20976↓0.24↓18.0 years
"Whenever this creature deals combat damage to a player, that player discards a card."
Pain Magnification82%
$0.83↑#13277↓0.59↑20.5 years↑
"Whenever an opponent is dealt 3 or more damage by a single source, that player discards a card."
Blim, Comedic Genius82%
$0.27↓#11422↓0.315.9 years↓
"Flying"
Chilling Apparition80%
$0.31↓#26842↓0.65↑26.4 years↑
"Whenever this creature deals combat damage to a player, that player discards a card."
Okiba-Gang Shinobi80%
$1.06↑#10175↓0.57↑21.7 years↑
"Whenever this creature deals combat damage to a player, that player discards two cards."
Fell Flagship80%
$0.36#12660↓0.07↓9.1 years↓
"Whenever this Vehicle deals combat damage to a player, that player discards a card."
Infernal Kirin80%
$2.30↑#17103↓0.19↓21.4 years↑
"Flying"
Wei Night Raiders80%
$34.89↑#25805↓0.51↑27.5 years↑
"Whenever this creature deals damage to an opponent, that player discards a card."
Liliana's Reaver80%
$0.28↓#9898↓0.3713.3 years↓
"Whenever this creature deals combat damage to a player, that player discards a card and you create a tapped 2/2 black Zombie creature token."
Screeching Buzzard80%
$0.04↓#27326↓0.11↓24.0 years↑
"Flying"
Banshee of the Dread Choir79%
$0.87↑#12896↓0.14↓10.9 years↓
"Whenever this creature deals combat damage to a player, that player discards a card."