Rakso makes some good points, especially about the Hypnotic Specters and Megrim.
I still play with my Megrims, but often found myself waiting to have Megrim(s) in play before playing any discard (BAD idea). This wasted any advantage early discard spells could give me. My solution was to add 4 Anvils of Bogarden (rare from Visions -- artifact, 2, each player draws 2 cards and then chooses and DISCARDS a card during his draw phase). This keeps the discard going, allowing the Megrim to work far more often. It is also less random for you than the Bottomless Pit.
A card that fits the deck could be the almighty Avatar of Woe. With a discard strategy, you can quickly fill graveyards with enough creatures to allow the ACC. If forced to hardcast the Avatar, it is still a great card, and easily done with your Basal Thrulls. Along with this is the idea of playing some form of graveyard manipulation (Animate Dead, Dance of the Dead, and Reanimate all let you in ANY graveyard -- Reanimate is my preferred choice).
Consider also Ravenous Rats. They are cheap to cast and force a discard when they come into play. Not bad at all.
Another option might be Ill-Gotten Gains, which forces all players to DISCARD their hand (then pull any three cards from their graveyard to be their hand) for 2BB. Unfortunately, its rare...
As for dealing with green, try Perish and the Western (or Eastern, I forget) Paladin. In fact, Persecute might work very well against known monocolored decks.
Overall, you have not enough creature removal. If you deal with small creatures, Massacre, Engineered Plague, (maybe) Extinction, and Thrashing Wumpus are good. If it's bigger creatures that ruin your day, try targeted removal, Terror, Expunge, Diabolic Edict, etc. Wall of Souls will slow your opponent down, as well.
If your opponent empties his hand early, and keeps it empty, far too many of your cards are wasted. While a spellshaper is not a bad idea for such wasted cards, in Greel's case, it defeats the purpose.
And for the record, despite its being banned in tourney play, Windfall is the best discard card out there. I use it in my multiplayer Megrim deck. The key is to bait the Disenchants with other enchantments...
That's all.