And the winner for most disgusting monster in all of D&D is...

This monster actually has a pretty good range of things it can do. You could even build this thing for melee and still come out okay, because its defenses are solid and its passive abilities are potent. I agree with Debatra that the atropal scion has hands and can wield weapons, so that helps it out too. Even advancing as a marshal with an undead army would be a pretty solid choice for this monster (if you're okay using almost exclusively passive abilities, and using your actions to command troops).

It will be tough fitting this guy into most parties, but when it fits with the party, it will be quite good. I think I'll agree with Efrate and vote LA +2 for the atropal scion. LA +1 might also work, but since it has a potentially volatile suite of abilities, I'd prefer to vote conservatively.