DedWards

Everything is weak to something, it's just the nature of the game. Now, you can include stuff to protect, OR you can include redundancy (which is what I went for). Splinter Twin was vulnerable to Path and Bolt, but that didn't stop it from being one of the best decks before its banning.

Stony Silence isn't too much of a problem either. With the exception of granting Battered Golem the tap to bounce ability, which can just be given to Mirran Spy, it doesn't affect the combo at all. Altar of the Brood is a triggered ability, not an activated ability. Stony Silence only stops activated abilities.

I've been having some success over the last month with my GR landfall deck:

http://www.mtgvault.com/dedwards/decks/gr-landfall-elementals-2/

Take a look, could help you with some ideas.

I will note though, I've tested both Grove Rumbler and Zendikar Incarnate and the Rumbler wins by far due to build in trample. with fetch lands, I've managed to get 4+ landfall triggers in one turn with regular success, making a 11/11 trampling Rumbler much better than a 8+/4 Incarnate without trample. Each fetch land = 2 triggers, followed up with land search cards like Explosive Vegetation is just bonkers.

I've also swapped out Nissa's Renewal in favour of Pulse of Murasa. The Pulse's interaction with fetch lands is excelent, and the fact that it's instant speed +6 life is just gravy :P

Mycoloth would be one of the first things I'd include. Rare dual lands and fetch lands too. Might even go 3 colours (thanks to the abundance of duals and fetches) to include some awesome white cards / cards that require white (Gavony Township and Ready // Willing comes to mind). And let's not forget Doubling Season.

Evolving Wilds to help with mana fixing.
Runechanter's Pike or Spellheart Chimera to take advantage of the ever filling graveyard.
Mana Leak; and Rune Snag are some of my favourite counter spells.

Good thing I already have a set of Hunted Horror :D

Hardened Scales

I just double checked, just to be sure, and you're right. Now I have even more reason to get Thing in the Ice.

Hunted Horror would be worth considering too. Thing in the Ice won't bounce it, but will bounce the centaurs it creates.

I'm not 100% sure Vampire Hexmage will flip Thing in the Ice.

"Whenever you cast an instant or sorcery spell, remove an ice counter from Thing in the Ice. Then, if it has no ice counters on it, transform it."

The "Then if" part of its transformation has me concerned about the interaction with Hexmage's removal effect. The clause has me thinking that the last counter removed must be done via its own ability for it to transform. I could be wrong though and Hexmage does allow it to flip, just saying that a ruling may be required.

Hardened Scales - boosts the number of +1/+1 counters.
Evolving Wilds - helps with mana fixing
Blossoming Sands - helps with mana fixing
Enduring Scalelord - with two of these out, they can get indefinitely big.
Inspiring Call - card draw and protects your creatures from most removal.
Managorger Hydra - gains +1/+1 counters whenever any player casts a spell.
Sunscorch Regent - gains +1/+1 counters and gives you 1 life whenever an opponent casts a spell.

I'm surprised no one mentioned this. You can double up on Voyaging Satyr with Kiora's Follower. Just like the satyr, it can untap Nykthos, but unlike the satyr, it can also untap Karametra's Acolyte. The Follower even adds the same amount of green devotion.

Don't forget Surgical Extraction to get rid of those things that shuffle back automatically.

The Altar would supply a nice alternative win.

Zulaport Cutthroat and Blood Artist die to Heartless Summoning, that's why I suggested Falkenrath Noble.
I also suggested Krark-Clan Ironworks as you can loop Myr Retriever in the same way with it.

In addition to Hedron Archive and Hedron Crawler, aother mana acceleration Artifacts you may want to consider is Seer's Lantern.

Paradox Haze is an awesome card. You currently have 8 cards with upkeep triggers, so I'm not sure if it works here. It's awesome when you do have those 8 cards, but when you don't, it's effectively a dead card. I'm not saying that you shouldn't use it, in fact it'd be awesome if you do use it, I'm just warning you of the possible down side.

I recently had success with Mutilate in my Korlash deck. -1/-1 per swamp you control to all creatures is actually pretty great, especially against creature heavy / dependent strategies.

Most people will suggest Painter's Servant to combo with Sphinx's Tutelage. While this is a good combo, I like the idea of combo'ing it with Teferi's Puzzle Box to increase the number of cards you draw each turn, thus making more triggers for Sphinx's Tutelage :P

or maybe Braid of Fire?

Just thinking now, Resonator makes the Honden from Kamigawa just a little better. I already use Paradox Haze with them, but Resonator can be pretty cool with them, and the mana required to play the Honden means that you should easily have {2} open in your upkeep (when the Honden trigger). In fact, the Honden deck I run requires so much mana that I run a set of Honor-Worn Shaku; which effectively allows me to tap the Honden for {C} each, easily supplying mana for the Resonator.

Searching for Bitter Ordeal is important. Dimir Machinations provides the same Transmute trick here. I also mentioned Beseech the Queen already, and there's always the classic Diabolic Tutor.

Maralen of the Mornsong could be useful too.

Also, Infernal Tutor can help fetch the second Myr Retriever.