I'd suggest adding 4x Sylvan Caryatid , maybe 2x Voyaging Satyr to untap Nykthos, Shrine to Nyx . 4x Polukranos, World Eater and 4x Arbor Colossus always. Go to 1x Nylea, God of the Hunt . 4x Genesis Hydra with this kind of ramp along with 4x Chord of Calling gets you any one-of you want. Which is why I'd suggest a Hornet Nest or two. Also, mainboarding 2x Nissa, Worldwaker would make your deck much better. A good way to get some card-draw going is maybe a one-off Life's Legacy . 2x Sylvan Primordial is also an amazing answer to anything normal creatures can't touch, Detention Sphere , planeswakers, and such. 4x Mistcutter Hydra sideboard. I would also probably straight up drop Deadly Recluse , Reverent Hunter , Kalonian Tusker , definitely Kalonian Twingrove , Aspect of Hydra , and probably also drop Hydra Broodmaster . Bramblecrush and Nylea's Disciple are also solid sideboard cards for this layout. Just suggestions, of course. I'm not trying to talk down to you or anything, I just want to help.

This is what I'm talking about: http://tappedout.net/mtg-decks/green-m15-x/

Looks goodi'd do the following:

• 4 Karametra's Acolyte
• 4 Elvish Mystic (which you've already done)
• 4 Sylvan Caryatid
• 4 Courser of Kruphic (which has already been done)

• 4 Voyaging satyr (you know what I'm gonna type)

• That sorts out the mana based creatures, as for big creatures id suggest creatures like Worldspine Wurm and Terra Stomper for this deck, the wurm is rotating soon but is an amazing card on the field and is very hard to remove, if they doom blade it or something, so what put it back into your deck, chuck down genesis hydra with god knows how many counters due to your ramp and easily chuck it down again :D p.s id also run 4 polukranos and genesis hydra

Your other big stuff is spot on

• 4 arbor colossus is great, gives off 3 devotion and is 5 mana for a 6/6 reach!!

• The kalonian twin grove is good in this deck, id run a few more maybe 3-4 because if you get it onto the field using lands its 6 mana for a 12/12 essentially which is good, i would suggest nissa world waker because she gets all forests out and 2 20/20's are very fun ;)

• If you want to run mist cutter as a creature instead of sideboard id run 4, this deck is all about getting insanely big things out, if you want bodies look into soul of zendikar but if your running them in the main board then 4 mist cutter would be wise, also 3 nylea is fine but id suggest to run 2, its more of a support card for game finishers, genesis can get her out if you want to finish the game but thats from my experience.

• Bow is good keep with it

• The aspect of hydra is a good card, i would suggest running 4 of it in the main board, unravel the aether is a tricky card to decide, its good at getting rid of pesky banishing lights but if your not against blue or white then it won't be useful whatsoever, id suggest side boarding them

As for the mana curve it looks great!

I plus 1 your deck. However I believe I have a few good suggestions. I think 4x Sylvan Caryatid is a must have in any green based deck. Its hexproof and mana ramps you. I also suggest running Chord of Calling as you are allowed to fetch with this card similar to Genesis hydras fetch ability. AlsoHeroes' Bane is so good late game whenever you need a fatty and you have tons of mana available. You can beef him up so huge with nykthos + voyaging satyr. Also Back to Nature is good for enchantment removal. I don't feel like arbor colossus is necessary. I saw this deck earlier today lets play fetch though it has blue splashed in, I think it's worth checking out. Maybe you can get some ideas from him or her. Sorry so long of post. Happy tapping :)

Thanks for all the comments and suggestions guys, I'm really starting to like the way this deck is looking!

Your welcome :) hope I helped some :)

Dude a sick card in any hydra deck would be Solidarity of Heroes I would also swap out Unravel the Aether for Naturalize but that's just me. for your side you might also want to consider the aforementioned back to nature.

Bro, hydra deck, and barely any good hydras, get somebody like a Heroes' Bane or Primordial Hydra then to take advantage of devotion, use a Primalcrux then a Khalni Hydra to add even more devotion

Open just saw standard, nevermind

Considering the nature of the deck, maybe think about dropping the two Bow of Nylea and mainboarding two Chord of Calling. Otherwise, I like it a lot.

I would definitely add a Heroes' Bane because during the late game you have insane amounts of mana flying around and nothing to dump it into.

See the Unwritten over Chord of Calling

But I am still testing.

Here's my version, a little different spin, but similar base. I like 4 Voyaging Satyr and 4 Nykthos, Shrine to Nyx with 3 each Elvish Mystic and Whisperer of the Wilds.

My deck: