River Sneak {1}{U}
Creature — Merfolk Warrior
This creature can't be blocked.
Whenever another Merfolk you control enters, this creature gets +1/+1 until end of turn.
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Cards that do something similar expected a card that isn't here?
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Forerunner of the Heralds 89%
$0.45#9224
"Whenever another Merfolk you control enters, put a +1/+1 counter on this creature."