Ertai's Scorn {1}{U}{U}
Instant
This spell costs {U} less to cast if an opponent cast two or more spells this turn.
Counter target spell.
click a line to search just that ability, click more to combine them
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.
Once Upon a Time 81%
$1.45#8818
"If this spell is the first spell you've cast this game, you may cast it without paying its mana cost."
Delightful Discovery 80%
$0.27#15894
"This spell costs {1} less to cast for each spell your opponents have cast this turn."