Shadow's Corrosion

This card can't be played from the EX area.
At the start of your end phase, if this card is in your EX area, deal 1 damage to each enemy leader for every 5 Natura cards in your cemetery.
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Select an enemy follower on the field. Deal it 4 damage and, if there's a Valdain, Cursed Shadow on your field, put this card into its owner's EX area.