The Prevenience set has a cycle of rare "Leech" creatures. Each one "leeches," for itself or for its controller, some ability or condition that is applicable to another creature or player. Each Leech also makes spells of a particular color one colored mana cheaper to play. The five Leech creatures are Dazzling Leech, Omnipotent Leech, Reaver Leech, Sylarian Leech, and Draining Leech.
* This cost-reducing ability is mandatory and affects all players. A player can't choose to pay the unreduced cost.
* This ability reduces the total cost of the spell in the appropriate color, regardless of whether the spell's controller chose to pay additional or alternative costs. For example, whether you play Flood of Anger by paying its {3}{R} mana cost or by paying its alternative cost ({1}{R} and discarding two cards at random), one Sylarian Leech in play causes that spell to cost {R} less.
* Sylarian Leech's ability reduces only the colored portion of a red spell's cost. A Goblin King (which normally costs {1}{R}{R} to play) would cost {1}{R} with one Sylarian Leech in play and would cost {1} with two or more Sylarian Leeches in play.
* Unlike most other cost reducers, a Leech doesn't affect the colorless mana portion of costs, even if the player chose to pay that portion with red mana. A Gambling Ogre (which normally costs {2}{R} to play) would cost {2} with one Sylarian Leech in play and would still cost {2} with two or more Sylarian Leeches in play.
* Sylarian Leech doesn't reduce a red spell's mana cost or converted mana cost. It simply lets a player pay less for a spell of the right color.
* This ability can lower the cost of a spell of that particular color to zero, but not below zero. For example, with a Sylarian Leech in play, Goblin Traitor would cost {0} and T.N.T. (The New Threat) would cost {1} to play. On the other hand, paying the alternative cost of Lightning Strike with a Sylarian Leech in play would still cost {0} and discarding a card at random.
* A Leech can't affect its own cost.