Birds of Paradise, Llanowar Elves, Elves of Deep Shadow, Elvish MysticTurn 1 Time Walk. To drop one of these on turn one is ideal, to draw them late in the game not so much. I am still not sure about what the right number to run of these in the deck is, but right now I am happy with these four.
Deathrite Shaman
This card is pretty reliable, at least for my metagame, since a huge amount of players use fetchlands or selfmill strategies, which turns on the mana producing ability of Deathrite. Sadly I do not have the 9:3:3 mana base yet. His other two abilities are very relevant, not for the loss of life or lifegain, but as graveyard check. A lot of people I play against take advantage of very specific cards in their graveyard, like recuring Mindslicer every turn or casting Turnabout multiple times, so I want to stop them in their tracks!
Joraga Treespeaker
A green version of Sol Ring. It can produce on the next turn if you level it up when you play it. If you drop it turn one and level it up on turn two, it feels a lot like Sol Ring. The other levels do not really matter though.
Blood Artist and Zulaport Cutthroat
With creatures to sacrifice left and right these can grant you a fair amount of value. You might need to compensate for some loss of life from cards like City of Brass or Necropotence, so incidental life gain does not hurt (no pun intended). In addition to this they can cause infinite loss of life in combination with the before mentioned Food Chain combo.
Sakura-Tribe Elder
This guy is just a synergistic Rampant Growth. He sets up your mana nicely and can be used with cards like Smothering Abomination or Grave Pact to great effect.
Sylvan Caryatid
Because of its hexproof ability it is an untargetable mana producer and can also stop early aggression due to its 0/3 stats. This thing is just a stronger but more expensive version of Birds of Paradise.
Fauna Shaman
This elf is a reusable creature tutor that can cycle a creature card in your hand for a card you need every turn? Whats not to love about this card? It might be a little worse than Survival of the Fittest, but it is very strong nontheless.
Reclamation Sage
Aside from the beautiful artwork this shaman can destroy problematic artifacts or enchantments while he adds another body to the board. The upside it has in comparison to other removal spells in the deck is that it is a creature, which means that it can be searched up with the various creature tutors like Worldly Tutor and Fauna Shaman if you need it.
Nissa, Vastwood Seer
She works almost like a Spellskite. People just target her with their removal spells because she has the word planeswalker written on her back. She is also a really nice value engine later in the game, draws cards, ramps ahead and spitts out 4/4 elementals. The forest she gets is nice as it ensures that you hit your landdrops.
Somberwald Sage
Second only to Ancestral Recall Black Lotus is the most powerful card ever printed. Now you get one every turn if you have Somberwald Sage. This thing allows for some really broken plays and is one of the reasons that this deck can win so fast.
Eternal Witness
The Witness will most certainly draw you a card that you actually want. She is a nice ensurance to get back Food Chain if it gets destroyed. Is there any green deck that does not have Eternal Witness?
Courser of Kruphix
This may be a worse version of Oracle of Mul Daya, but filtering the lands from the top of your deck means that you do not have to waste draw steps on them. Incidental livegain is pretty great in a deck that has cards like Necropotence, Phyrexian Arena and similar cards in it. It even has synergies with the fetchlands in the deck!
Falkenrath Noble
A more expensive version of Blood Artist, but still a fairly strong card. It can go infinite with the before mentioned Food Chain combo.
Smothering Abomination
When this card works, it is the single best draw spell in the entire deck. If it does not, it can fling right back in your face. But even with that risk remaining the Abomination is too good not to run. Since Prossh generates many tokens you always have some creatures to sacrifice so you can draw a card with the Abomination. I you really need to keep your creatures on the board, you can just sacrifice it to itself to get rid of it.
Purphoros, God of the Forge
What if I tell you that there is a Theros god that deals 14 damage to every opponent whenever you cast your commander and even more damage whenever you cast it again? In addition to that Purphoros can cause infinite damage in combination with the before mentioned Food Chain combo. It pairs really well with Avenger of Zendikar.
Ogre Battledriver
This is the best haste effect in the entire deck! But not only does he grant haste, he gives a +2/+0 bonus to every creature that enters the battlefield! This thing is like a mini version of Overrun. Cast Prossh and go nuts!
Oracle of Mul Daya
An elf that ramps you several turns ahead and ensures that you always draw into gas has to be great. It gets rid of lands on top of your library and is amazing with fetchlands.
Sidisi, Undead Vizier
An undead naga that serves as a Demonic Tutor on a stick that also adds a 4/6 body with deathtouch to the board and has synergy with sacrifice effects? You can even sacrifice it to itself if you have no other creature to sacrifice on the board! This card has a sure place in this deck!
Zealous Conscripts
Its main purpouse is to go infinite with Kiki-Jiki, Mirror Breaker but it is also able to steal a creature for one turn which will then be sacrificed to one of our outlets after hitting its original owner.
Kiki-Jiki, Mirror Breaker
The wet dream of every combofile!
Xenagos, God of Revels
Aside from making Prossh a lethal thread he can pump up any other creature in the deck if you are on the beatdown plan. An indestructible enchantment is virtually impossible to get rid off, so Xenagos will probably stick once he hits the board. If your opponents have cards like Path to Exile, be aware of his devotion and make sure that it does not reach 7 to keep safe.
Butcher of Malakir
A Grave Pact on a stick! This card just takes the boardstates of your opponents and flushes them down the toilet. A 5/4 bodt that swings in the air can do some serious work. Search this up at instant speed with Chord of Calling for extra fun!
Avenger of Zendikar
A nice backup win condition in case our combos do not work out. This angry elemental will unleash an army of plants against your opponents that will only grow as the game goes on.It basically is your second impression of Prossh in the deck.
Atarka, World Render
In the case you need to rend some worlds, Atarka is ready to do what Gruul does best:
SMASH FACE !!!
Craterhoof Behemoth
This card is often times the last card played whenever it hits the battlefield, since the game is most likely over shortly after. Its boost usually exceeds lethal amounts and even a couple of tokens can end the game when this monstrosity stomps onto the battlefield. With only eight mana casting cost it is not unreasonable to assume that you can hardcast it reliably, but you can also cheat it out with cards like Pattern of Rebirth for even more ridiculousness.