I've been playing Monogreen since Garruk dropped in M13 and haven't looked back. I've dabbled in splashing black and blue at different times, but keep coming back to red while Xenagos, the Reveler is around. Here's the card & sideboard breakdown:
Arbor Colossus: With the meta being what it is, pretty much every tier 1 deck has a flyer in it's stash. I find it's worth keeping 2 main board because, even if they don't, he still adds 3 devotion and is a 6/6 beater for 5.
Courser of Kruphix: Thin the deck, help know when to pop the Genesis Hydra, and add 2 devotion. Plus he can block Brimaz and some of the Jeskai wimps easily.
Elvish Mystic: While they aren't as pivotal as the other ramp, it's still a great T1 move to help you put out your other ramp or the Courser quicker.
Genesis Hydra: Most ramp decks run 4 of this guy, but I find running 2 and using the other 2 slots for Chord of the Calling fits better with needing to find my answers more consistently. I run two because it pairs with Courser well, but too often does Chord get me out of problems, flashing in Reclamation Sage on g2/3 or Hornet Queen to stomp the Roc/Rider/Butcher.
Hornet Nest: More often than not, my opponents either use a burn spell on this guy, which keeps my beaters alive longer, or they are too scared to swing without trample. Very effective addition.
Hornet Queen: My pride and joy. I'll play this card until I die. The devotion is enough to make me weep while the tokens are just gorgeous as they make your opponent weep.
Nissa, Worldwaker: I keep 2 main board because of the heavy control meta. Using her +1 again a Perilous Vault is an incredible feeling.
Nylea, God of the Hunt: Easy to grab with the Chord or Hydra and just finishes the game with her +2/+2 ability.
Polukranos, World Eater: I know most people are phasing this guy out, but with his monstrous ability destroying aggo decks and his defense against the Rhino, I can't find a good reason to part with him.
Rattleclaw Mystic: Less versatile than the Caryatid, but being able to swing with him is helpful at least once a match. Plus, without ramp, my deck is a snoozefest, so having every bit of help I can is pivotal.
Sylvan Caryatid: Arguably the best 2 drop in the game.
Xenagos, God of Revels: 10/10 Polukranos on t3 or 4? Gladly. Another finisher.
Xenagos, the Reveler: Ramp ramp ramp until you can ulti him ASAP.
Crater's Claw: Don't be afraid to use this on their beaters. Ramping it to 11 to their life is a sweet feeling, but keeping yourself alive is just as important as the big plays.
Sideboard:
Arc Lightning: Jeskai's worst nightmare and a great 2nd main phase twist in g2.
Nylea's Disciple: Great in anything that runs long as well as aggro decks.
Plummet: Just in case you need more help.
Reclamation Sage: Destroys Courser or any other enchantment creature as well as their Whip, Banishing Light, or Perilous Vault.
Setessan Tactics: Great in a mirror match or just anytime you need your hornet to kill their Rhino.
Unravel the Aether: More control and aggro hatred.
I've spent a long time on this deck, but I want it to wreck. And no, I'm not doing constellation or Stormbreath.
