Mystic Remora
Enchantment
Oracle Text
Cumulative upkeep
(At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays 
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Rules for this card
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A keyword ability that imposes an increasing cost to keep a permanent on the battlefield. See rule 702.24, “Cumulative Upkeep.”
Rulings (2)
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Wizards of the CoastCumulative upkeep is a triggered ability that imposes an increasing cost on a permanent. "Cumulative upkeep [cost]" means "At the beginning of your upkeep, if this permanent is on the battlefield, put an age counter on this permanent. Then you may pay [cost] for each age counter on it. If you don't, sacrifice it."
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Wizards of the CoastPaying cumulative upkeep is always optional. If it's not paid, the permanent with cumulative upkeep is sacrificed. Partial payments of the total cumulative upkeep cost can't be made. For example, if Mystic Remora has three age counters on it when its cumulative upkeep ability triggers, it gets another age counter and then its controller chooses to either pay or sacrifice it.