I thought about that too of course. Basically I'd say fueling them isn't bad at all, one simply has to make sure the sacrifice isn't too cheap. So I was thinking about maybe modifying it to "Sacrifice a worthy creature: [...]", with "worthy" being all creatures but skeletons and magn. cells. Yes, sacrificing could still be an advantage all in all (BW, BY, Vulture...) but it would be very hard to get those sacrificable creatures.
I could also just change it to Darkness though. Aaand I have to think about if it's too close to your card. Maybe I'll open a poll.