Suggestions....


Scarland Thrinax -> Phyrexian Altar.
Still an instant-speed sac outlet, but it gets you something useful! This has the potential for some really silly plays with Prossh.


Hua Tuo, Honored Physician -> Demonic Tutor.
Hua Tuo is very narrow, D-Tutor is anything you need it to be! Especially key combo pieces! 


Kresh, the Bloodbraided -> Mana Echoes.
This plus the Altar goes unfinite with Prossh (both in casts, tokens, and mana). Even without the Altar, casting Prossh with this out (the first time) nets you 36 colorless mana. 


Mycoloth -> Sprout Swarm.
Mycoloth is a slow, durdley card. Sprout Swarm can also get you a large number of tokens, for a lower cost, and at instant speed. 


Champion of Stray Souls -> Lightning Greaves.
He's big and slow, and speed is what you have been looking for. Lightning Greaves will let you start swinging Prossh as soon as he hits play for more out-of-nowhere kills.


Hydra Broodmaster -> Diabolic Intent.
Demonic Tutor #2, and sac'ing a creature is no biggie for you. In fact, it's probably is helpful.


Eater of Hope -> Attrition.
Once again, same effect. Cheaper to cast, cheaper to activate.


Fated Return -> Reanimate.
It's all about cutting down mana costs, and it's hard to beat 1 mana.


Spoils of Victory -> Cultivate.
Same cost, but it's a better card. 


Untamed Wilds -> Rampant Growth.
You usually wont get the benefit of the land coming into play untapped. Rampant Costs less, and ramps into a better turn 3. 


Ob Nixilis -> Exsanguinate.
Obie makes opponents think twice about going and grabbing a card, but Exsanguinate threatens to end the game right now.


Obelisk of Jund -> Banefire.
3 for a 1 mana accel isn't that great for this deck. And while Banefire might not be as game-ending as the previous card, it's almost impossible to stop. Protip: aim it at the blue player.  


Deathrite Shaman -> Exploration.
Just a preference. Exploration turn 1 gets pretty nuts. 


Sylvan Caryatid -> Oracle of Mul Daya.
Caryatid is ok, but will probably die at some point. Then you are down a land, basically. Oracle comes out later, but can help dig and is really good friends with Top.


Mogis, God of Slaughter -> Birthing Pod. 
Mogis is pretty cool, I'll admit. But people will usually take the 2 (which isn't much) or sac a useless token. Pod adds a ton of consistency, trust me. 


Scavenging Ooze -> Courser of Kruphix.
Scooze isn't a bad card, but Courser is basically another Oracle of Mul Daya. He'll dig you deeper and net you some life in the process.


Stalking Vengeance -> Acidic Slime. 
You aren't running a ton of huge guys, you need more answers to things, and a more 5-drops will help your Birhing Pod chain.