Channel

Sorcery    (CMC:2)

Until end of turn, you may add colorless mana to your mana pool at a cost of 1 life per point of mana. These additions are played with the speed of an interrupt. Effects that prevent or redirect damage may not be used to counter this loss of life.

3E • ENRichard Thomas

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Legal in: Freeform,Prismatic,Singleton 100

Oracle Text (click to copy):

10/4/2004
You can't pay life you don't have. In other words, you can't Channel yourself below zero life.