Cemetery Prowler

Vigilance
Whenever Cemetery Prowler enters or attacks, exile a card from a graveyard.
Spells you cast cost {1} less to cast for each card type they share with cards exiled with Cemetery Prowler.

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Card types that can be exiled from a graveyard include artifact, creature, enchantment, land, planeswalker, instant, and sorcery. Legendary, basic, and snow are supertypes, not card types. Human, Equipment, and Aura are subtypes, not card types.

Cemetery Prowler's last ability checks the number of card types among cards exiled with it, not the number of cards exiled. For example, if Cemetery Prowler has exiled two creature cards, creature spells you cast cost {1} less, not {2} less.