I have to agree with what Essence and PuppyChow have said.
Rainbow has its true strength in being able to use any of the cards in the game. This gives you an enormously wide variety of 1) Creatures, 2) Spells, 3) Permanents, 4) Weapons, 5) Shields... From my experience, most rainbows contain Otyughs (Gravity) and Fallen Druids (Entropy/Life), and then Boneyards, Bonewall - to make the most of creature control. Then, put a couple Empathic Bonds on top of that, so that you can have a chance to survive with no shields. The obvious Firestorm/Rain of Fire is the 'most effective' creature control card available.
So, to build a Rainbow-Poison/Time deck, like you said... will be an extremely difficult task. Poison very rarely - on it's own - manages to do even a full 100 damage to an opponent during a game... Let alone the 200 (sometimes 600 or more, against Miracle) you will need to do.
Until there is a card which played once, deals accumulative poison damage on your opponent, I don't think Poison will have a very impressive Win-Rate against the False Gods.
I'll go to the trainer and try a few things out, but overall, I'm doubtful.