While Spinning Darkness can't hit players, the bonus life it gives you while killing a creature essentially for free is priceless
The next variant is a customizable enchantment that allows you to hurt a particular race: Why does R&D make cards that hose the theme they're trying to push
flipping a card face-down doesnt cause it to change zones, so it doesnt go back to the command zone unless somebody trades for it
Commanders like Jenova, Ancient Calamity are always good, because you don't necessarily need them on the field for the build to work, but they offer consistent value
There are all sorts of wacky combos you could do with this, so youre only really limited by your imagination
Generally speaking, there should always be more cost 1 cards than cost 2 cards, more cost 2 cards than cost 3 cards, and so on and so forth