Enchant player

As this permanent transforms into Curse of Leeches, attach it to a player.

At the beginning of enchanted player's upkeep, that player loses 1 life and you gain 1 life.

Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

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Lifelink

Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)