OmniscientMastery

Solid list. I like dropping the nebelgasts and two selfless spirits for the playset of supremes.

Just a heads up: Oloro is not actually modern legal due to his only printing being in a supplemental product. Just find a suitable replacement for him to make this modern legal.
Regardless, this seems like a very fun deck. Maybe you could find some room for a mind stone or signet? Your curve seems a little high with the majority of your spells on 4 mana. Modern is a fast format, so you need to look to get your payoffs quick.

Nice! I hadn't considered Shu Yun or Brute Strength in my prowess deck. Unfortunately Monastery, Shu, Wild Slash, and Fetch Lands rotate out pretty quick.
Suggestions would be Slip Through Space and maybe the new Sin Prodder.

(^.^) Let's do this.
-2 Reef Worm. Too slow for legacy!
-4 Fog
-2 Darkness
-4 Mana Leak
-2 Preordain
-2 Damnation
*-2 Breeding Pool (unless "budget")
*-2 Overgrown Tomb (unless "budget")
*-2 Watery Grave (unless "budget")
-4 Birds of Paradise
- 3 Spell Pierce (counterspells are good, but we're looking more towards hand disruption)
That's a lot of minuses, but let's see some of the replacements!
+2 Sylvan Library for card selection/advantage
+2 Duress to remove key cards from their hand
+2 Inquisition of Kozilek (see above)
+4 Thoughtseize (see above)
+4 Crop Rotation in order to find Dark Depths
+1 Dark Depths in order to find more Dark Depths
+4 Urborg, Tomb of Yawgmoth in order to allow more access to black (and turns on Dark Depths for mana)
+4 Lotus Petal as a faster replacement for Birds of Paradise
*+2 Tropical Island
*+2 Bayou
*+2 Underground Sea

These are the recommendations I'd make!
Additionally, if you do want some form of protection to keep Dark Depths around (you want to), -4 ponder and add in some Daze, or Not of this World, or even Sejiri Steppe!

Ok, I'm not the best at *turn creatures sideways* decks, but I enjoy commander, so I'll give this a go.

-8 land, you are currently 12 cards over the limit. This will only put you 4 over.
Less equipment. While your creatures are your main win condition, they are either sufficient in size or buff each other well enough to avoid the necessity of additional interference. At roughly 1.5 spells per turn, an artifact can feel like a dead play when you'd much rather be on pace with another creature.
Ramp: drop doubling cube, and gilded lotus. You are a two color deck, color fixing should come easy. Also, you neither combo off, nor need a massive swing in mana from the cube. Replace them with a Mind Stone and maybe a Solemn Simulacrum or Worn Powerstone?
Goodbye Helvault. Goodbye Staff of Nin. I personally don't like Helvalut, and I think Staff of Nin is not the 6 drop of choice, especially with your *curve*.
Assuming you only dropped Loxodon Warhammer and Sword of Vengeance from your list, you should now be at 99 cards.
If you did drop the remaining Swords and Batterskull, you could potentially bring in the additional cards you have in the sideboard if you desired this route.

Once again, I'm not especially skilled with crafting beatdown decks, but these would be just a few changes I'd make to have this deck in a playable state.

Really? It seems our play group will have to reevaluate how we've interpreted that ruling.

Yes, you can Dash Zurgo from the command zone without having to pay the additional 2 mana for each time you've cast him.

Avacyn, Angel of Hope would be a good addition. She instantly protects Kalia on her swing to keep her from dying to a block etc. Also, all of your other permanents are indestructible as well, how useful.
Also, Ionia, Sheild of Emeria is great in commander, due to its ability to nearly shut down one color. Another great addition, if you like it.

I won't tell you which cards to remove if you'd like to make room, because you and I might have different ideas for this deck!

Please, for the love of soul sisters, find room for Soul Warden and Soul's Attendant.

Forgive my ignorance, but is Kataki, War's Rage not a viable sideboard card, or if so, when would you run it as opposed to Stony Silence?
Edit: I might have solved my confusion. Affinity could just sac everything to Arcbound Ravager and pay only (1).
And here I thought I was clever. Thanks anyway!

Oh wow, I guess it's been a good month since I've been on, and I actually forgot I posted this.
I'm glad for the discussion stirred by my comment, and the many intelligent arguments given.
I'm so pleased to hear that I'll finally get to experience the mythical forums I've heard so much about after nearly 3 years on the vault!
I appreciate what this site has helped me do for my enjoyment of the game, and am always glad to see it improved!

And not a single NorthernWarlord deck...

With what black mana will you cast disregard or cut?
I don't see any here.

Formatting Tip: Move your Commander to the sideboard in order to better communicate that fact to your viewers.

Could you post your sideboard so that I may glimpse the unthinkable nature of this competitive mill?
I'm trying to build a Mill deck myself, and I am torn between whether I should plan for removal or simply try to outspeed their Aggro with my spells. The deck can mill as early as turn 4, with a consistent turn 5-6 win. It rarely takes longer than 7 turns, but this is a bit slow in the modern meta. The sideboard would be appreciated!
This deck has earned a like from me.

Just a few suggestions/questions.
How has only 17 lands been working? I prefer at least 19.
Blood Moon has always seemed to me a sideboard card. Perhaps run Scalding Tarn so you can fetch your basic lands before you drop a Blood Moon to not hurt yourself if you don't have Islands.
I'm also not too keen on Vapor Snag, but as far as big creature removal goes it'll do. (I run a Grixis Delver, so I have access to terminate! XD )
If I were to make changes, I would drop Vapor Snag altogether. I would Bring Dispel up to mainboard and drop Blood Moon to sideboard. I would drop 1 Sulfur Falls and 1 Island, and then run a set of Scalding Tarn. (I would also wish for all the money required to make these changes :(. )

However, those are just personal preferences and I would like to say that I like your build! You've earned a like from me.
But for real, how smoothly does just the 17 lands run?

I was going to mention this!

Or now you have an indestructible 5/5 creature that could still tap for a land if needed?

I love the vintage basic lands to go with the vintage commander! Nice work.

Scalding Tarn isn't standard legal (yet... fingers crossed)