You need more ramp, so try adding Birds of Paradise or Sylvan Caryatid . Arbor Elf isn't going to do much alone.
Also, you really need Karametra's Acolyte + Staff of Domination , and switch out Magus of the Candelabra for the Acolyte.

I also have a few questions:

• How competive does your deck want to be?
• Do you want to add in blue, to make more options?
• Have you thought about using +1/+1 enchantments like Doubling Season or Hardened Scales for more counters?

Finally, you really need to protect yourself from board wipes!

Very good points! Thanks for the comment. To the questions, yes, I do want this to be fairly competitive. I have thought about and tested out splashing blue or white or even red to allow for more options, but I've never found something that doesn't begin taking away from the main theme. I've thought about having +1/+1 enchantments, but at that point I think a higher priority would be to add a protective enchantment in something like Asceticism or Privileged Position . I do agree with having more ramp, and I thought about switching out the Magus of the Candelabra for 2 more Garruk Wildspeaker . However, I do like the Sylvan Caryatid a lot. Maybe because of the theme, Karametra's Acolyte would even be a better option. I used to run them in here but took them out. I think Staff of Domination could add potentially an infinite amount of mana, but my only worry is that at that point, what will I spend it on? I've run into having far more mana available than needed many times with this deck. I think what I'll do is switch 2x Magus for 2x Acolyte. I would love to throw in one of the two hexproof enchantments I mentioned, but I'm just not sure what to take out at this point. I did have to throw in Hunter's Insight just because the card draw is so needed so badly.

Thanks so much for the advice! I'll make the initial changes then I'd love to hear more advice based on my answers to those questions!

Infinite mana on Polukranos! Or Vastwood Hydra ftw!
Anyway, maybe Primal Rage for the trample, or Rogue's Passage for unblockable?

I do already get trample on Primalcrux and Kalonian Hydra . And Nylea, God of the Hunt and Garruk Wildspeaker give trample to everything. But, I do really want to put at least one Vastwood Hydra in the deck. I'm just not sure what to take out honestly. Maybe I'll take 1 Aspect of Hydra out and 1 Kalonian Hydra out but I don't know. They both seem so crucial. Any suggestions on what to take out? I really just need to make space for these things because I also wanted to put in something like Asceticism or Privileged Position into the deck.

Maybe take out an Ooze or Hunter? It won't be necessary to have 4, as it will hurt your curve.
And add more ramp! Maybe have Search for Tomorrow instead of Overgrowth?
Is your deck on a budget?

Okay, So I took out 1 Kalonian Hydra , 1 Predator Ooze , 1 Aspect of Hydra , and 1 Mosswort Bridge to add 2 Vastwood Hydra and 2 Asceticism . And no, it isn't on any kind of budget! So welcome any kind of expensive additions if they are truly better and needed. I think in terms of ramping, I've got things covered in the ramping section of the description.

If it's counters you're looking for, then Increasing Savagery is a great way to get a ton on the board.

Good point! I decided that the 2x Asceticism can be on sideboard to swap in 2x Increasing Savagery . I think I ought to almost always have enough mana mid-game to play it and then play its flashback.

Primordial Hydra instead of 1x Geist and 1x Vastwood Hydra?

Thanks for the comment! I actually really like the Primordial Hydra ; I think I'm going to swap both Vastwood Hydra 's out for that.

Add Solidarity of Heroes and Gyre Sage to double your counters and get more mana!

Great suggestions! I'm going to replace Increasing Savagery with Solidarity of Heroes. Gyre Sage looks great, but after some playtesting I've done with the deck, mana isn't too much of a problem right now.

Maybe Torpor Orb in your SB?
What about a Staff of Domination for infinite mana?

Ah, yeah I really need to develop a sideboard eventually.. probably will consider Torpor Orb in that, although it hurts Reverent Hunter quite a bit.

Staff of Domination requires that I have an Arbor Elf down and a forest that is producing 4 mana, which only keeps tapping and untapping the staff and elf. Unless I had more than 4 mana production off an enchanted forest (which is possible), then it's a hard situation to come by. Plus, if I can get 5 or more mana off of one "super enchanted" forest, then with an arbor elf, 10 mana is plenty. Cool thought for sure though! Am I missing anything obvious in my reasoning? If so please let me know cause my brain is on about half function right now.

If you had a bunch of green devotion (at least 5+), and had Karametra's Acolyte out, then you could eventually net out mana with Staff of Domination:

1) Tap Acolyte to get 5 mana
2) Tap Staff for "3, T: Untap target creature". You have 2 mana, but you have untapped Acolyte.
3) Pay 1 mana, and untap Staff. You now have 1 mana in your mana pool.
4) Tap Acolyte for 5 mana. You now have 6 mana in your mana pool.
5) Repeat.

I see what you're saying, it would just be a dead draw unless I had met that condition already. Honestly, if I have enough forest enchantments out and/or the Acolyte with 5+ devotion, I will have already attained a huge advantage. At that point, my concern would more-so be focused on getting card draw (Which is why I put in Hunter's Insight).

Got it...
What about Reclamation Sage in side instead of Seal of Primordium?

Interesting idea! There are pro's and con's to both, but as I think about it more, the Sage does seem to fit better! Good suggestion, I'll make that switch!

What does Thrun, the Last Troll do in your SB?
Also, your deck can destroy Affinity, but what about some lifegain against Burn? Predator's Rapport, perhaps? And how do you protect the creatures?

Might take Thrun down to one (he is good though against control/discard). Scavenging Ooze is great lifegain. Could also consider Kitchen Finks, Obstinate Baloth, or Thragtusk for lifegain. I think having the Baloth would make me able to take that place of Thrun.

Also considering Skylasher against any control or blue variant.

Ok, made some updates. I think against burn, I've got some pretty good resiliancy:

Scavenging Ooze, Obstinate Baloth in SB for lifegain against direct burn. But in MB, most of my creatures can take a bolt: Kalonian Hydra and Karametra's Acolyte both have 4 toughness, Nylea, God of the Hunt and Predator Ooze are indestructable, Primalcrux takes at least 2 bolts if not way more (hopefully), and Strangleroot Geist comes right back for another bolt (which is half their bolts, well kinda).

What do you think of the SB now as a whole against all matchups?

SB seems good so far, but what does Skylasher do???
Have you thought about splashing in blue?

Skylasher goes in very well against blue control of any kind, whether that be UW control/midrange or UWr control or even combo decks with blue counterspells like Splinter Twin decks etc.

Also goes well against any deck with blue creatures or even just flyers. This isn't a super common threat in modern, except for well, oh, just Delver of Secrets  ^Flip which is coming back so strong. Because it has protection from blue and is uncounterable, it can freely block, not get blocked, or get removed by any blue sources.

But to clarify, it doesn't have to do with me playing blue, but rather it's a reaction card for when my opponent is (that's what sideboarding is about).

Sorry, I meant that did you want to splash in blue or white for more potential? Blue gives you unblockable/hexproof/counterspells, White gives you Archangel of Thune and Path to Exile.

Believe me, I've considered just about every color splash, and there are two big problems with all of them:

1) There isn't much outside of green that fits with the theme quite as well (mostly the fact that I'm trying to build up devotion, so having a white/blue/etc. permanent doesn't do any good there).

2) Land base for multi-color... For competitive in modern it's super expensive. It would likely double this deck's cost.

As much as I would love to utilize some other colors, I just can't see it working out. Although I do have some other pretty good multi-colored decks on my page if you wanna check em out!