Desecration Demons are good, but you would bee better served putting in straight removal,
Hardened Scales, or mainboarding the Bioshifts. Seccondly, its the only spell that costs double black to play, so without it, you can treat black as a splash color and add things like
Golgari Rot Farm,
Llanowar Reborn (good land tech, since the graft ability makes more +1/+1 counters available to you) as more land tech. Otherwise, this seems like a solid deck.