
VigilanceVigilanceAttacking doesn't cause this creature to tap.
EerieEerieAbility word: triggers whenever an enchantment enters under your control and whenever you fully unlock a Room. — Whenever an enchantment you control enters and whenever you fully unlock a Room, put a possession 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 an X/X blue Spirit creature token with flying, where X is the number of counters on this creature.
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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.