You could consider Treacherous Pit-Dweller.

Eldrazi Mimic is pretty good with Phyrexian Dreadnought.

Cut Watery Grave, add more fetches for shuffle effects with Brainstorm/Top.

I added Bloodstained Mire and Flooded Strand for more shuffle effect.

You will never need the black on its own so Misty Rainforest or Scalding Tarn does a better job.

Does this deck seem to flood very often? If so, you may be able to cut down on some lands to add more discard or a Gitaxian Probe/Cabal Therapy package since there is some synergy doing that if you have a Treacherous Pit-Dweller in play. Since nothing here costs more than 2, I can't imagine a time where you'd need more than 3-4 lands in play.

I have contemplated adding Probe/Therapy combo but I've found through my play testing that 20 lands seems to be the sweet spot for the deck.

That's understandable. If you did decide to add the combo, it looks like the MD extractions and possibly the lotus petals would be the cards to cut. You would be sacrificing explosiveness for disruption, but since I'm not familiar with the deck I wouldn't be able to offer my opinion on which direction would be better.

Oh, I love this deck so much..

My deck is a variation of this combo and its so fun to play..

I'm just thinking, isn't Hunted Horror better than Treacherous Pit-Dweller?

I know there is the Undying, but a 7/7 Trampler is quite stronger than a 4/3 or 5/4, what do you think? Worth testing?

I love my deck! Very fun one to play.

I used to use Hunted Horror but I found that Treacherous Pit-Dweller was quicker and easier to cast in most situations. The real heavy hitter is Phyrexian Dreadnought anyways.