Call for Blood 

Instant — Arcane
As an additional cost to cast this spell, sacrifice a creature.
Target creature gets -X/-X until end of turn, where X is the sacrificed creature's power.
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Cards that do something similar 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.
Fungal Infection 91%
$0.15#15270
"Target creature gets -1/-1 until end of turn. Create a 1/1 green Saproling creature token."
Take the Fall 91%
$0.13#14685
"Target creature gets -1/-0 until end of turn. It gets -4/-0 until end of turn instead if you control an outlaw."
Peppersmoke 91%
$0.25#15398
"Target creature gets -1/-1 until end of turn. If you control a Faerie, draw a card."
Faerie Fencing 91%
$0.26#7966
"Target creature gets -X/-X until end of turn. That creature gets an additional -3/-3 until end of turn if you controlled a Faerie as you cast this spell."
Induce Despair 91%
$0.10#27835
"Target creature gets -X/-X until end of turn, where X is the revealed card's mana value."
Eye Gouge 89%
$0.06#28161
"Target creature gets -1/-1 until end of turn. If it's a Cyclops, destroy it."