ClockworkCopper

Boseiju, Who Shelters All would be a nice addition in your sideboard for control decks.

Being a five drop I would run Leeching Sliver over Thorncaster Sliver, Also Diffusion Sliver and Sliver Legion are great choices. Also a nice combo I found is Ghostflame Sliver then followed by a All Is Dust.

Give it some time my FNM they are starting to pop up more and more. It's easy to run, cheap, and very affective. I mostly been running a Green, Red, Black decks mostly based on quick creatures and planeswalkers and still it struggles against aggro red from time to time found out the best cards putting them to a halt are Circle of Flames and Hornets Nest but, be careful Hall of Triumph has been seeing some play in there sideboards to step over Circle of Flames.

I would maybe take out Coastal Piracy you have Bident of Thassa already in this deck not sure if the enchantment is needed. In Garruk's Wake is nice but, a little to expensive for nine mana so maybe could take that out. Also instead of Beseech the Queen I would run Demonic Tutor. Turn Aside is more for single matches not sure if you are a group player or not but, is most group games most people run board wipe removal so not much in single targeting unless a Path to Exile or Swords so that could be an idea as well.

Well put, Æther Vial and Boseiju, Who Shelters All would become nice additions to your sideboard incase a Force of Will or counter hits the field. Was also thinking Path to Exile maybe a better choice, use it on your opponent creature before land destruction hits or if needing a land yourself exile one of your creatures for the land. Oh, and running white Flagstones of Trokair would be great, you could search for a Godless Shrine, Scrubland or a Plains when it hits the graveyard.

Deck seems very fast paced aggro, I would run Mana Confluence over some of your tap lands. Being able to play your colors needed at an early start without having to follow next turn for tapped lands. I know life loss kind of sucks but, life is nothing more then a resource as well plus, playing Sorin, Solemn Visitor you should be able to gain it back.

I like the idea only thing I could suggest is Sylvan Caryatid. Additional mana ramp, early blocker, hexproof, and adds any of the three color combinations.

Mutavault works very well with Gravecrawler (in case you don't have a zombie in play). Tap it to activate it's self then being able to play Gravecrawler from your graveyard being that Mutavault is all creature types. Also it gets past counter decks and can become a 2/2. Another idea for control decks and counters is Æther Vial being as most of your creatures are one to two drops.

I found that Circle of Flame in sideboard works very well with any fast aggro creature decks such as fast white and black creatures and mono red aggro/burn. It doesn't stop then all out but, slows them down.

Running Purphoros as your commander Glitterfang, Grinning Ignus and Norin the Wary come to mind. Pretty much playing them triggering Purphoros ability dealing damage to your opponents, then repeat, also both are pretty cheap for the wallet.

I like the idea with Nekusar, the Mindrazer and Waste Not, nice. I would maybe run more group drawing maybe Howling Mine, Burning Inquiry, Dictate of Kruphix, Font of Mythos, or Kami of the Crescent Moon. These would deal more damage with Nekusar, the Mindrazer in play also overdrawing would make them discard and with Waste Not in play giving you the advantage.

Thraximundar would be a nice addition also Solemn Simulacrum. I would also maybe go with another board wipe or two maybe Damnation. You can wipe the board and your creatures would come right back into play. I noticed that many of your creatures are four or more to cast I would possibly go with more mana ramp like Sol Ring, Coalition Relic or Chromatic Lantern. Maybe a lot to take in but, hope this is helpful, other then that deck looks great.

Æther Mutation comes to mind but would need to run blue. Other then the two you listed not sure if there is that many cards with that ability.

Other ideas Doomed Traveler, Elspeth, Sun's Champion, Hornet Nest, Lingering Souls, Night Soil or Pharika, God of Affliction (If run black), Raise the Alarm and Precinct Captain. Also buying some time before playing Sigil Captain, you could add Pendelhaven.

Splashing black, Bitterblossom and Abzan Ascendancy comes to mind.

Heres my take on Nahiri, the Lithomancer if interested, been getting some play in with her when have the time so still in the test cycle.

http://www.mtgvault.com/clockworkcopper/decks/nahiri-the-lithomancer-edh/

A Commander deck would be interesting to see you do though. Sigil Captain is a good choice for a deck way back in the day I ran him with a bunch of 1/1 mana dork elves and Coat of Arms.

You could try a standard and EDH deck.

This may seem far off but, you could also run Faithless Looting into Enter the Infinite when you have Possibility Storm in play. I thought also at one point Squadron Hawk be a nice addition for more of a filter searching for Emrakul but would require white. And on the white aspect Curse of Exhaustion would lockdown your opponent from being able to Possibility Storm themselves.

Also Pit Fight or Prey Upon maybe a nice addition in your sideboard incase going against zoo decks, show and tell or any large creature based deck. Just think before attack step Pit Fight a Emrakul, the Aeons Torn with Hornets Nest then blocking it killing it with a deathtoucher.