I was excited to see you made an EDH deck that doesn't look like it would make me want to crawl under the table and cry. Then I saw Iona, Ruric Thar and an eldrazi and realized you didn't!

Why no Sol Ring, though?

No shock lands?

I considered a sol ring, will probably put one in there still. But I have a lot of mana ramping in the deck as it is. And shock lands would be nice. I just don't have any right now. Nor do I really play with them..

You have some really nice cards here, and with a little work this could be a very sick deck. Marath is by far my favorite Commander to play.

You really need Spike Feeder to go with Archangel of Thune - infinite health and infinite counters on all your creatures.

Purphoros, God of the Forge - is great when you are pumping out tokens. Basilisk Collar is amazing on your commander. Spot removal on a stick.

Illusionist's Bracers is great also. It's a mini doubling season... almost. Keep in mind that once you have a counter doubling effect you can add counters back to Marath and grow him bigger.

Skullclamp and Mentor of the Meek - cause extra cards off your 1/1 elementals is good yah?

You need some enchantment/artifact removal maybe Return to Dust, Acidic Slime or Woodfall Primus.

Path to Exile and Swords to Plowshares if you have white in your colors you should be running these, no buts - make room for them. You should think about adding at least 1 board wipe. I run Terminus because, well its good, and it gets indestructible creatures.

I know extra mana is great, but cards that give your opponents that same benefit need to go. More mana for you - good, more mana for opponents - game losing bad.

Your land need some real work. I know its pricey, but it's well worth it, even adding them one at a time. I recommend 38 to 39 lands, 35 with no mana rocks seems like you will get mana screwed too often. You can't cast ramp spells if you don't get any mana.

Recommended lands:

Fetches - Arid Mesa, Windswept Heath, Wooded Foothills

Pain lands - Battlefield Forge, Karplusan Forest, Brushland

Check Lands - Clifftop Retreat, Rootbound Crag, Sunpetal Grove

Shock lands -Stomping Ground, Temple Garden, Sacred Foundry

Utility - Gavony Township, Oran-Rief, the Vastwood

Ok, I've preached on long enough. If you have the time you should check out marcagel on youtube, He runs a Marath deck on MTGO and has some great ideas. Seeing it played helps it all make sense.https://www.youtube.com/channel/UCacNtD8m5TqaaoYTHXpVPAg

Have fun and have good draws