Cavern Whisperer 

Creature — Nightmare
$0.17 #9951 0.24 6.4 years
Mutate 
(If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Menace (This creature can't be blocked except by two or more creatures.)
Whenever this creature mutates, each opponent discards a card.
Click a line or tag to filter
Cards similar to Cavern Whisperer 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.
Silent Specter84%
$0.53↑#23044↓0.80↑23.9 years↑
"Whenever this creature deals combat damage to a player, that player discards two cards."
+1 more matching line
Caligo Skin-Witch84%
$0.17#24368↓0.158.4 years↑
"When this creature enters, if it was kicked, each opponent discards two cards."
Mournwhelk84%
$0.29↑#24904↓0.53↑18.9 years↑
"When this creature enters, target player discards two cards."
Cao Cao, Lord of Wei83%
$5.21↑#22408↓0.71↑27.3 years↑
"
: Target opponent discards two cards. Activate only during your turn, before attackers are declared."
Scepter of Fugue82%
$0.35↑#25977↓0.3117.6 years↑
"
,
: Target player discards a card. Activate only during your turn."
Liliana's Specter82%
$0.14↓#98070.60↑16.1 years↑
"When this creature enters, each opponent discards a card."
Ashiok's Adept80%
$0.16↓#24121↓0.53↑12.6 years↑
"Whenever you cast a spell that targets this creature, each opponent discards a card."
Herald of Anguish80%
$0.36↑#112490.67↑9.6 years↑
"At the beginning of your end step, each opponent discards a card."
Stony-Voiced Goblins80%
$0.26↑#20009↓0.00↓0.1 years↓
"When this creature enters, each opponent discards a card."