Heh, anti-Devotion before Devotion existed. "You want to cast your Phyrexian Obliterator? Hope you didn't really want your land base anymore..." This card is pretty fun, especially if you have some colour-changing effects (since you can change "black" to "green", but they'll still have to sack Swamps). But, unless you have a colour-changing effect, it's pretty useless against non-black decks. I'd run this with Swirl the Mists for maximum fun.
Pros: Screws over black decks hard
Cons: Only useable against black decks without support, upkeep cost
NOTE: Check the errata'd text on this before decrying my idea as "non-functional"