Sweet deck !
Why do you have Distress in your deck if Thoughtseize is strictly better ? I would also switch Sign in Blood for Painful Truths as it allows you to draw more cards. Beseech the Queen is also worse than Vampiric Tutor. Orcish Lumberjack might be a very sweet card if you want to have fast mana , but you would have to put a few more Forest into your deck. If you do not mind infinite combos , you could put Earthcraft and Squirrel Nest into your deck. Also Food Chain is probably the strongest Combo card with Prossh. If you do not know how these work, you can look up my decklist, I wrote a little section about how to use them. Assault Strobe grants Prossh double strike, thus making one attack with him lethal damage. Xenagos, the Reveler can produce giant ammounts of mana if you activate his +1 after you cast Prossh. Also you are playing Duel Commander, which means that you can take advantage of powerful cards like Primeval Titan, which is probably one of the best green creatures ever printed. I hope these suggestions were a little helpful.

Thanks for the feedback TheDracogenius.

I have Distress in there simply as temporary budget replacement for Thoughtseize. I have been focused more on updating some of the overall ratios of cards and land base before I start putting too much money into better versions of the cards I have.

Painful Truths is a card I had seen at one point while updating the deck but completely forgot about it, Sign in Blood was a card I just happened to already own.

I like the idea of Orcish Lumberjack as it would also fit with my goal for a turn three Prossh, however I simply don't run enough forests to make him viable.

Earthcraft + Squirrel Nest is good but I don't think I would be able to reliably get it off with the number of basic lands I run. I also have a hard time running two cards that will most likely only be used for the combo, if I run any infinite combo it will most likely end up being Kiki-Jiki, Mirror Breaker + Zealous Conscripts .

I like Assault Strobe and used to run as many cards like that as possible. I have since tried to get away from relying on Prossh for a lethal swing and instead have been diversifying my win-conditions. I may use it instead of Tainted Strike as it could have more utility throughout the game, however whichever one I were to use will eventually be replaced with Berserk once I can afford it.

I originally had Xenagos, the Reveler in here. I loved how his +1 worked so well with the theme of the deck and that his second ability produced tokens for blocking/feeding Prossh, I was never able to use his last ability in a game but it usually wouldn't be worth using over his +1 anyway. The only problem I had was he couldn't really ramp to get Prossh out earlier than the T1 dorks and after I cast Prossh I am hoping to win in one swing.

Oh Primeval Titan, one of my favorite cards. I was so disappointed when he first got banned and was equally excited when I found I could use him in duel commander. I of course put him in at first without a moments hesitation, but after playing for a while soon found that I almost never cast him. His mana cost was simply too high for anything other than late game ramp or to search for specific lands. I already had enough ramp at lower mana cost for both early and late game and I really don't yet have any lands worth consistently searching for other than Kessig Wolf Run. Once I am able to get Wasteland, Cavern of Souls, Gaea's Cradle, or Maze of Ith it would be more viable but I am more likely to just use Crop Rotation.

Vampiric Tutor, Food Chain, and so many other cards I would like to run are banned in duel commander.