One more thought: Jalum Tome. I get a ton of work out of it in my black green deck. Gets rid of unwanted land draws and puts big creatures you can't cast into the graveyard for reanimation.

How 'bout some sedge trolls to go with those earthquakes?

Onulet is terrible. I think royal assassin is a much better 3-drop -- most opponents HAVE to deal with it and it gives you a repeatable sac outlet. I'd consider adding there.

My first impression is you have more sac outlets than you need. I would also toss some of these cards for being weak or lack of synergy. Maybe temporaily move onulet, fork, Su-Chi, terror, shatter, and greed into your sideboard and see if you can replace them with more powerful cards. This deck is slow, so consider dark ritual and bolt.