This is definitely an interesting card. First, it's like Phyrexian Processor in the sense that it turns your life into a creature. Now, this card does have trample whereas the Minions don't, but this isn't very repeatable unlike the Processor. Also, there the restriction of "you can't pay more life than the total number of white cards in play on your opponents' sides and in their graveyards" which is fairly weird and might mean that it might be very small. All in all, it's a decent card for a decent price.
Pros: Black creature with trample, turns life into creature
Cons: Restricted by number of white cards
One final note on this card: to my knowledge it is the only creature card in Magic without a creature type. If you check to Gatherer rulings for this card here, you'll see a 2007 ruling that says "this currently has no creature type" which I think is pretty neat!