For the low, low cost of one card, you get to attack again, draw a card, and use all of your mana a second time, plus get a crack at additional upkeep/end step triggered abilities and all that good stuff
It's best in multi-colored decks as it will discount the spell by two mana, assuming the spell has the two colors you named in its casting cost
We also simplified Hades by trading the copying ability to one that let you play cards from anywhere
So if you, for example, wanted four copies of Double Colorless Energy in five different decks, you would need twenty copies
First of all, keep in mind that all Un-set questions are always up to interpretation, and may be played different by different playgroups