Despair

I love this deck, Kulrath Knight is such a pain to deal with, always love to see shriekmaw getting used instead of straight up doom blades or terrors.

To be perfectly honest i'm not sure why you have Urborg in here, you'd be better off running two more cabal coffers instead.

Again i really like how this deck looks, seems like its synergy will be absolutely awful to play against, props to you sir

Ahhhh, evil elementals are an old favorite of mine! :D
This deck has alot of things that make it quite competitive, especially the creatures mana curve is almost exact with aether vial, and your counter output is solid and capable with black suns zenith able to kill weaker horde based decks. Though your sideboard is empty, and a deck like this has a few basic cards that can be used(:

However, before the sideboard can come into play, there are a couple weakpoints with in the deck D:
first and probably the only one is: Sickle reaper.
This deck has so many other cards that can benefit it so much, such as aether vial should be a definite three in the deck because you play alot of three and four cost creatures, which would consistently be put on the field with rituals and the vial. Sickle reaper is a nice quick little wither hitter, but he's too weak in the deck to be put in over another necroskitter, or maybe another zenith. :/

So, I would cut down the sickle reapers to maybe two or none at all, and add in one more crumbling ashes or necroskitter and one more aether vial(:
(-2 sickle reapers, +1 aether vial, +1 necro skitter, -2 swamps, +2 cavern of souls)
caverns of souls is just the perfect land for this deck and your dark rituals and basic mana cost plus the aether should save mana and supply enough for your enchantments since they both have blank mana with in them(:

The next thing, since you wrote in your description of a tournament this is competing at, is the thing I hate most... Side boarding! :D
Legacy is a format that has some powerful things. This deck is gonna have a hard time with quick horde build ups which can quickly be solved with sideboarding two more black sun zeniths into the deck, to give you a nice field wipe that works with crumbling ashes and necro and blowfly ^_^
Next, I would sideboard (presuming you play three allready) a single necroskitter for an opponent whos gonna wanna play some big ass green creatures.(Or god help us...eldrazi D: ) lol, so getting a kill card in with necro on the field after zenithing or anything along the lines will completly end the game, giving you the instant advatange ur opponent has wanted all game(:

Also, once again for horde decks, black suns zenith should be boarded for something like a kuldotha goblin, or some fast explosive horder, whilst side boarding maybe two crumbling ashes or just one would help against white horde decks that slowly build some sort of indestructible thing or try and lock down the field with a sudden timely reinforcements or a isochron+raise the alarm. Once a single token is killed with a token, you basically just wiped the field one creature after one creature after another :D
Its like dominoes with field wipe ^-^
(Also if they ahve some ridiculous basic creature horde deck like slesnya, side board one or two kulrath knights for contrl aspect(:
And last thing that comes to mind, is maybe side board four scars just for a deck that is very single creature based like an isntant delver/kami of the moon deck or something along those lines (:

Besides all of that, thats all I gotta say about elementals(:
I made an elemental deck that got pretty popular(70+likes) a while back, one of my favorite decks I have actually and I'd be interested in ur opinion of it or if it inspires you to change this deck at all(:
Post in the description how you do and good luck with glourious black :D

http://www.mtgvault.com/greenee/decks/the-elements-are-tainted/ -the deck