Snag 

Instant
You may discard a Forest card rather than pay this spell's mana cost.
Prevent all combat damage that would be dealt by unblocked creatures this turn.
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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.
Hunter's Ambush 89%
$0.10#20030
"Prevent all combat damage that would be dealt by nongreen creatures this turn."
Harmless Assault 88%
$0.11#24924
"Prevent all combat damage that would be dealt this turn by attacking creatures."
Submerge 88%
$7.04#4314
"If an opponent controls a Forest and you control an Island, you may cast this spell without paying its mana cost."
Commencement of Festivities 87%
$0.18#14574
"Prevent all combat damage that would be dealt to players this turn."
Defend the Hearth 87%
$0.07#14602
"Prevent all combat damage that would be dealt to players this turn."
Druid's Deliverance 83%
$0.33#4041
"Prevent all combat damage that would be dealt to you this turn. Populate."
Deepwood Legate 83%
$0.16#23900
"If an opponent controls a Forest and you control a Swamp, you may cast this spell without paying its mana cost."
Rushwood Legate 82%
$0.27#29487
"If an opponent controls an Island and you control a Forest, you may cast this spell without paying its mana cost."
Dolmen Gate 82%
$31.59#1338
"Prevent all combat damage that would be dealt to attacking creatures you control."