ClockworkCopper

Nice deck I have thought about making an EDH deck around Shirei, you could try running Magus of the Abyss, Smokestack or Contamination for added sacrifice or freezing up there mana production.

Kiln Fiend would be great in this deck, also what about Magma Jet dealing two damage as well as scrying or browbeat for an added five damage or drawing three cards either way a great choice.

If you would like you can also check out my Omnath EDH deck for any ideas.
http://www.mtgvault.com/clockworkcopper/decks/omnaths-revenge-edh/

I forgot about Jolrael, Empress of Beasts, I will try him out as an added back-up not very excited about the discarding part but does make all lands as 3/3 creatures in one clean sweep. Also a nice mana production artifact is Gauntlet of Power one less to cast then Caged Sun and Bane of Progress of crazy good against artifact decks and enchantments.

Omnath is one of my favorite EDH generals, one of the best cards I find that works great is Kamahl, Fist of Krosa. He makes everyone think twice about board wiping creatures.

Gray Merchant of Asphodel perhaps?

I am liking the mill ability you have going on here.

I would say instead of running Chorus of Woe I would go with Signal Pest 44 cents a piece isn't bad plus the ability stays well, until the Pest dies.

Instead of Riot Control I would go with Druid's Deliverance instead, it's one less to cast and it has populate so either with your Armada Wurm or Advent of the Wurm you can prevent the damage plus add another 5/5 wurm to your army.

I would run at least two Asceticism giving them hexproof and regeneration, also Dolmen Gate would be great giving the fact they have trample another idea is Bow of Nylea assigning one damage to the creature blocking and trampling over with the rest. Not sure if Bellowing Tanglewurm is that great, one it will become a large target, and two doesn't do much if the other player is running green at best I would add it in your sideboard. I would take out:

-3 Descendants' Path (because if you draw more all they do is sit in your hand)
-2 Bellowing Tanglewurm
-4 Woodland Changeling's

Then add:

+1 Garruk, Caller of Beasts (just like Descendants' Path but more of a drawing idea plus final ability is great)
+1 Bow of Nylea
+2 Asceticism (Protection is always a must)
+1 Dolmen Gate (Dealing damage and not being dealt damage)
+4 Adaptive Automaton (One more to cast but being able to give all your Aurochs +1/+1 for added damage)

I hope this helps out, in any way.

Well, Buried Alive works great with Gravecrawler because you can play it from your graveyard so all you have to do is search for the Gravecrawler's then play them right from your graveyard, (as long as you have another zombie into play).

What about running some thoughtseizes great for those tricky cards and adding cards to there graveyard. Also, hero's downfall for some Planeswalker's removal. There is also Breaking on the card Breaking/Entering eight cards for two mana is pretty good.

Have you thought about running Buried Alive works great with your Gravecrawler's, searching for three then bring them into play. Also Carrion Feeder goes nuts with Gravecrawler's by using them as an added feed engine put +1/+1 counter on him.

Why not run a Whip of Erebos or two? Works great with reanimating your Gray Merchant's (with added life gain and life loss) or Demon's plus giving all your creatures lifelink is always an added bonus.

So far what I got is this deck is revolved around getting out Kalonian Hydra, I see your mana ramp seems to be fast not sure if you are needing the blue in this deck like Omenspeaker could easily be replaced with Magma Jet doing damage, and Scry for 2. Another thing you don't really need the four bows I know there awesome but being Legendary if you draw any others its a dead draw and they mostly just sit in your hand so may go with two at the most. Also, basing a deck on a fatty like Kalonian he is going to become a major target so Hexproof would be a must like some cards would be like Alpha Authority or Ranger's Guile. Also a great card with Kalonian I have found is Savaging Ooze or any smaller creatures that can enter with +1/+1 counters so not only Kalonian is getting counters so are the rest of your other creatures. I am running a solid green deck in standard and got 2nd so feel free to check it out for some more ideas if you would like, but hope this helps you out.

Nice idea with this demon deck, I see your playing Treacherous Pit-Dweller's have you thought about tossing in a few Homeward Path's so if they come back you can return them back to play on your side instead of giving them to the other player.

I see it is one of my favorite combo if your interested feel free to check out my Leveler deck I will list it below.

http://www.mtgvault.com/clockworkcopper/decks/the-leveler/

Playing with Dark Depths it maybe wise to toss in a Lightning Greaves or two so when he hits the field going in for an instant attack plus not being the target of spells and abilities is always a plus.

Have you thought about adding a Laboratory Maniac or two, playing Leveler in this deck with Laboratory Maniac in play is an instant game winner.

I know you are mostly basing around zombies but have you thought about a few Consuming Aberration in your deck would become a very large creature quick plus has an added nice milling ability.