Dictate of the Twin Gods absolutely wrecks in this deck with a Purphoros, God of the Forge out and Deathbringer Thoctar

Also Destructive Flow is pretty hilarious, as long as you have Xenagos to counteract the mana loss

Beastmaster Ascension and Fresh Meat work great in this deck. Grave Pact and Dictate of Erebos are also awesome. And adding Purphoros, God of the Forge makes Prossh just explode.

Defiler of Souls is pretty cool as well.

I get good results out of Grave Pact, Dictate of Erebos, and/or Butcher of Malakir partnered with Attrition or the Stronghold Assassin you already have. You add Blood Artist and/or Falkenrath Noble you have a party. For flavor...
Mycoloth, for plenty of greens.
Hellion Eruption, cause it makes me laugh.
Rancor for the Endless Cockroaches.
Thatcher Revolt for Human Sacrifice.
Putrefy, Cause it's better than Murder.

Xenagos, God of Revels let's Prossh kill a player the turn you play him. Just make sure you eat Kobols pre-combat and clear out any fliers. Of course the moment Xenagod hits the board everyone is gonna throw out whatever they can block with cause you may surprise someone once, but after that they'll see it coming from a mile away. Also Xenagod and Purphoros are so good because if you don't turn them into creatures they are nigh impossible to get rid of.

Thanks PrecintSix6Six, super helpful. I will add him to my list. I am getting Skullclamp and Beastmaster Ascension off a friend, but a lot of these cards are really hard to get because my playgroup banned buying singles. If you guys know other products that have any of these cadrs that would be super helpful.

Banned buying singles!?! That complicates things. Look at Planchase deck Primordial Hunger. It's a G/R Devour deck featuring Mycoloth, Thromok the Insatiable, and a few other token producing cards that compliments Prossh nicely.
I got my copy of the Hellion Eruption I mentioned above from that deck.
Everything else I can think of would be like buying the 2013 Core Set Mob Rule intro pack for Krenko, Mob Boss and Krenko's Command. Not very cost efficient.

Thanks BigHairyGM. It will definitely be my next purchase. Dragonlair Spider, Mitiotic Slime, Mycoloth, Thromok the Insatiable, Awakening Zone, Fires of Yavimaya, Hellion Eruption, and Overrun will all be useful in the deck.

Also I have a friend with a Krenko, Mob Boss, but if not I will definitely consider the second purchase.

How can someone ban you from buying singles? That's just dumb, if I have the money and the desire to have it I'm going to buy it and no one can tell me otherwise, what are they going to do? Not let you play? That's bullshit I say fuck them buy the cards you want and if they won't let you play then you needed a new play group anyway!

Kozelek, I know it sounds stupid but there are many reasons we did, despite whether or not we realize now we made a mistake. There is not an LGS within 30 mins of where we live, first off, and second there was one kid we played with that bought singles, before we actually started caring about the game and at this point we've given him so much crap he would kill us if we unbanned buying singles. At this point it keeps our match ups somewhat fair, and keeps luck a big factor in who does well in our tournaments, rather than who has $150 to drop on fetches and duals. But thank you for the advice!

Banning buying singles is very odd but I can see why a group would do it. The way we deal with it is we have an unofficial spending limit. We don't buy singles over 10 dollars. Commanders are an exception. I just got Sliver Overlord to command my Sliver EDH. But as a rule if we have a high dollar item in a deck we pulled it from a pack.

baddabiiing: "Also I have a friend with a Krenko, Mob Boss, but if not I will definitely consider the second purchase"

I was giving an example of a bad cost/benefit ratio. If you decide you want to purchase a Krenko check out the Speed vs Cunning duel deck. I think you can get it cheaper than the Mob Rule Intro Pack.

Krenko, Mob Boss
Ogre Battledriver
Fleshbag Marauder
Reckless Abandon
Bone Splinters
Krenko's Command
Act of Treason
Fury of the Horde

Not Useful for Prossh,
Lightning Helix
Arcanis the Omnipotent

BigHairyGM Thanks, didn't realize that had Ogre Battledriver too. I will definitely look into that, pretty sure I can still get it for MSRP.

Skullmulcher.