Krovikan Mist 

Creature — Illusion
Flying
Krovikan Mist's power and toughness are each equal to the number of Illusions on the battlefield.
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Cards that do something similar expected a card that isn't here?
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Ixidron 81%
$0.37#7683
"this card's power and toughness are each equal to the number of face-down creatures on the battlefield."