I think what is much more interesting than his 5C is that he grabs cards when he enters the battlefield. Over on the cEDH discussions (well, I first saw it on the Facebook group), he is already talked as a wincon in Foodchain decks. Which makes totally sense even for optimized decks, as when your deck can make infinite colored mana with Foodchain, running him out and continually sac’ing him to find the stuff needed to close out the game is very solid.
So even if you don’t go cEDH, going full-on value deck with his 5c and having him as a card-selection engine to run out when the coast is clear sounds like a very nice plan. Far less build-around as the other Niv’s of note, and you couldn’t do those non-combo. But this one could easily be, by just using blink effects and such stuff to dig into your deck and pull out your 2c bombs.
The restrictions are moderate, because you can still run your mono-G ramp pieces easily, as you won’t grab them when he comes out anyway – and probably you want to run ways to grab as many of those as possible anyway. What I would do is use a ramp setup that uses green creatures and spells to grab lands and put them into play or hand, just to thin out the deck, and some creature tutors to pull those rampers out, too. Then have a bunch of guild-colored bombs to finish people off when you have everything setup nice and tight.
And well, I guess I would still put in the foodchain combo, but that’s just me being a filthy combo player đ