Counterbalance {U}{U}
Enchantment
Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, counter that spell if it has the same mana value as the revealed card.
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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.
Swindler's Scheme 95%
$0.17#22730
"Whenever an opponent casts a spell from their hand, you may reveal the top card of your library. If it shares a card type with that spell, counter that spell and that opponent may cast the revealed card without paying its mana cost."
Lavinia, Azorius Renegade 84%
$0.51#3154
"Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell."
Boromir, Warden of the Tower 84%
$5.62#837
"Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell."