Although, @WitchDoctor133, you might instead make it so that invoke makes the spell cost {1} more, instead, for each creature you sacrifice, and then give a similar but more powerful effect. Metaphorically speaking, this would probably equate to the powerful surge of energy bursting through the creatures, thus killing them in the process.It might already happen if a spell costs X, and then you sacrifice X creatures, but that's how a lot of keywords are made, isn't it?
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Here's what I came up with. I hope I'm not to late on this.
A new card!