Gravelgill Duo {2}{U/B}
Creature — Merfolk Rogue Warrior
Whenever you cast a blue spell, this creature gets +1/+1 until end of turn.
Whenever you cast a black spell, this creature gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)
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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.
Hydro-Man, Fluid Felon 90%
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"Whenever you cast a blue spell, if this card is a creature, he gets +1/+1 until end of turn."
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"Whenever a player casts a blue spell, this creature gets +2/+2 until end of turn."
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"Whenever you cast a noncreature spell, this creature gets +1/+0 until end of turn."