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Crystalline Nautilus

Enchantment Creature — Nautilus

Bestow (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.) When this permanent becomes the target of a spell or ability, sacrifice it. Enchanted creature gets +4/+4 and has "When this creature becomes the target of a spell or ability, sacrifice it."