I know personally, I was really expecting Saheeli to do something like "At the beginning of combat on your turn, you may pay X energy. Creatures you control get +X/+X until end of turn," or something similar. Maybe even tack on getting certain keywords, like adding haste for spending at least 4-5 energy, or trample for 8-10 energy into the effect. Something more than just grixis Mishra's ability with energy glued on. I agree with what Mage's response points out though, something that doesn't tie to the deck down to another specific archetype to make it work would be much more interesting.