The cEDH approach uses Rograkh as an easily-accessible piece of sac fodder for partner Tevesh Szat, Doom of Fools or a ritual like Culling the Weak
Kinnan, Bonder Prodigy takes a different approach than the 3 previous entries, electing to instead turbocharge your mana dorks, mana rocks, and any other nonland permanent you control that makes mana by enabling them to produce an additional mana of any type they produce
Wait, no, thats Rampant Growth
Seven mana does put this card on the backfoot for competitive viability, but Sin can be a rather serious Commander or reanimator target
Looking at this, I thought a lot about the most recent set excluding Final Fantasy, Tarkir Dragonstorm, and how this card fits in so well with those recently released decks and strategies
Im afraid this will end up a clunker, but its one of the splashier cards in Avatar: The Last Airbender