Hollow One
Artifact Creature — Golem
Oracle Text
This spell costs
less to cast for each card you've cycled or discarded this turn.
Cycling (, Discard this card: Draw a card.)
Rules for this card
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A keyword ability that lets a card be discarded and replaced with a new card. See rule 702.29, “Cycling.”
Rulings (4)
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Wizards of the CoastOnce you've discarded three cards during one turn, Hollow One costs
to cast. It won't stop at 
or cost negative amounts of mana.
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Wizards of the CoastHollow One's first ability doesn't give you permission to discard cards. You'll need another effect that instructs or allows you to discard them, such as a cycling ability.
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Wizards of the CoastTo determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Hollow One). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.
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Wizards of the CoastHollow One's cost is reduced even if the cards you've cycled or discarded aren't in your graveyard.