The trading card game Magic: the Gathering gained a popular new format in the early 2010s: Commander. First known as EDH, this semi-casual format is based on 100-card singleton decks, each led by a Commander that sets the deck's color identity and, often, its core strategy.
In the world of red-green, the most common strategies are based on big creatures, enchantment and artifact destruction, mana ramp, and "lands matter." A strong option is the Battle for Zendikar mythic rare Omnath, Locus of Rage. Although a seven-drop, this 5/5 Elemental is easy to cast in these colors, and its size and triggered abilities make it a heavy-hitting Commander. Let's review the basics of deckbuilding for Omnath.
Lands Matter
Omnath, Locus of Rage has two triggered abilities based on two major arenas: lands, and the Elemental creature type. Omnath decks ought to stick close to the average of 40 lands, but these are more than just Forests, Mountains and generic dual lands (though those are necessary).
Fetchlands of all types are powerful here, since each one can trigger Landfall twice: once from itself entering the battlefield, and again when you put the second land on the battlefield. Imagine playing a Wooded Foothills (one trigger), then cracking it to get a Stomping Ground (trigger #2). Myriad Landscape and Blighted Woodland fetch for two lands at once, so that's three triggers from each. Time these fetches so you get the most value out of all the land ETB triggers whether Omnath is on the field or not.
Other utility lands should also be present (such as Kessig Wolf Run and Skarrg, the Rage Pits) to boost a creature's power and give it trample. Man-lands, like Raving Ravine and Treetop Village, can double as creatures that survive boardwipes.
Creatures and spells can augment land-fetching both as ramp and to trigger Landfall abilities. Though expensive, Oracle of Mul Daya can get the job done. On a budget, Courser of Kruphix can do something similar. Sakura-Tribe Elder is a cheap staple, and as for instants and sorceries, turn to Kodama's Reach, Cultivate and Harrow.
Elemental Tribal
Omnath is an Elemental, and its second triggered ability applies not just to the 5/5 Elemental tokens that it creates, but to all Elementals that you control. This means that when using a wide variety of powerful Elementals (both low-drops and high-drops), some may strengthen each other or have "lands matter" abilities. Undergrowth Champion is a 2/2 Elemental for 1GG, it has Landfall and it is difficult to kill via combat damage.
Meanwhile, Zendikar Incarnate's power grows with the number of lands you control, Ingot Chewer smashes artifacts, Creeping Trailblazer can pump itself and all other Elementals, and Smokebraider can add a lot of mana to your mana pool if you're casting it on Elemental spells or their activated abilities. Magmaw is a 4/4 red Elemental that acts as a sacrifice outlet, and Whisperwood Elemental can make 2/2 Manifest tokens each turn.
Sacrifice Outlets
Omnath may not be a sacrifice-heavy deck, but this is an important subtheme due to its "whenever an Elemental you control dies" ability. It's a Lightning Bolt with each trigger, and if the board state stalls out, you get a lot of reach to your opponent's life total if you can make your Elementals die on command (or destroy certain creatures you don't like).
Red and green both have effective sacrifice outlets, such as Magmaw, Perilous Forays and Evolutionary Leap, not to mention Momentous Fall and Life's Legacy as one-time sacrifice outlets. These cards offer benefits aside from the Omnath trigger from dealing extra damage to gaining life and allowing you to draw cards. Instant-speed sacrifice is even better when an opponent uses a boardwipe or targeted removal. If your creature will die either way, sacrifice outlets are the better route.
The Rest
There is still room for an assortment of cards in between land fetch spells, Elementals and sacrifice outlets. A few planeswalkers can provide extra mana or synergize with land, such as Nissa, Vital Force or Xenagos, the Reveler. As for artifacts, try out the classic Crucible of Worlds, as well as Seer's Sundial, Sol Ring, and any number of mana rocks that make red-green mana. Equipment such as Blade of Selves, Lightning Greaves and Swiftfoot Boots can make Omnath better when attacking.
Burn spells are welcome here, especially those that can scale up, such as Mizzum Mortars (overloaded), Clan Defiance and Blasphemous Act (which can double as a sort of sacrifice outlet). Doubling Season makes Omnath a total monster, and Asceticism can make your creatures nigh-impossible to take out. Artifact and enchantment destruction also helps, such as Destructive Revelry and Reclamation Sage. With Omnath, humble lands aren't dead draws; they're your best weapons of all.