Kalonian Hydra would fit your +1/+1 counter theme.

I appreciate the suggestion, TheDuggernaughtbut I'd like to keep everything to a casting cost of 3 mana or less if possible.

Here is my budget-ier version: Cheap Greenies 2.0

I am a huge fan of Heroic Intervention, so I would definitely recommend it.

As far as the specific issue you mentioned, I would definitely pick Prey Upon. I have never been a fan of Beast Within. Any thought to Nature's Way? Big benefits for just one mana more..

shaistyone, I have to admit that Nature's Way does look awfully attractive. I'll have to ponder that and where it might fit.

Regarding Prey Upon, what do you think about Ulvenwald Tracker, which will let you do it at instant speed and repeatedly, though at greater cost?

Ulvenwald Tracker definitely seems worse to me. One of the biggest strengths of removal is how it helps you disrupt your opponent's gameplan. Having to wait for a fragile 1/1 body to survive gives them too much time to play around it and plan for it.
That said, test it out. I'd love to be proven wrong. :)

shaistyone, I'll be testing it out tonight. Honestly, I've been looking for another 1-drop to smooth out the mana curve in the deck and I figure, worst case scenario, it draws the targeted removal normally reserved for other, more dangerous attackers. With this deck I generally prefer a creature that does things over a spell that does things...

With either Ulvenwald Tracker or Prey Upon, it makes the inclusion of Rhonas the Indomitable that much better.

This deck looks very very interesting! I was scrolling through the advertise-your-modern-deck forum, and the name caught my attention.

What you currently have is good on it's own, but what I think you could do is adding more ramp. Gyre Sage doesn't look too bad, has evolve, and can tap for multiple depending on your evolve, but another guy you can use is something like Birds of Paradise, Llanowar Elves, etc. Your Dryad Militant doesn't look too efficient, unless the extra power matters for evolve, and Ulvenwald Tracker doesn't seem necessary, as you already have the pump to easily smash your opponent's creatures. Both seem like good sideboard cards, though. You could always lower the numbers.

The collected companies in your maybeboard? they can definitely go into your mainboard, as they can easily snag any creature you have, all at instant speed. I would also suggest card draw, but the only sources I can think of off the top of my head is Harmonize, Regal Force, and Elvish Visionary, and Inspiring Call, which all probably will not work out too well.

Do you really need 3 melira? You probably would only need that many if your meta had a ton of infect, and if so, running a set of coco would let you have only 1 or 2 melira.

If you’re interested in splashing red that gives you access too Grumgully, the Generous and Glorybringer

Otherwise consider Rhonas the Indomitable , Nissa, Worldwaker and Rancor

You might want to try Walking Ballista as a 4 of. its arguably the best mana sync creature in the format and can be used both offensively, defensively, and as each to finish off someone if the board state is clogged.

If you're going to run Karn in the side (honestly, I'd run something like Blossoming Defense or Heroic Intervention to protect your dudes), I would add a copy of Henge in the side as well, so that Karn can tutor for it. Also, you may want to look into cards like Pithing Needle or Phyrexian Revoker to deal with troublesome abilities.