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Couple this with the fact the card hasnt been reprinted outside of The List and a Pro Tour promo, and youve got a recipe for an expensive card
II Creatures you control get +1/+1 and gain double strike until end of turn
Cards that give +1/+1 counters are great when only your creatures are targets, but if you are trying to help get rid of a particularly annoying creature, you may not want to be giving your opponents creatures permanent bonuses
Legendary Enchantment Creature Horror3/3 Flying When The Master of Keys enters, put X +1/+1 counters on it and mill twice X cards