
This creature enters with a number of +1/+1 counters on it equal to one plus the number of other creatures you control.
AllianceAllianceAbility word: triggers whenever another creature enters under your control. — Whenever another creature you control enters, put a +1/+1 counter on this creature.
When this creature diesdiesA creature dies when it goes from the battlefield to a graveyard. Being exiled or returned to hand is not dying., create a 1/1 green and white Citizen creature token for each +1/+1 counter on it.
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Read from the rules text. A card that enables a keyword makes or is the thing; a card that rewards it gets better when you have it. Two cards interact when one enables what the other rewards.