https://infinite.tcgplayer.com/article/Competitive-MTG-Modern-on-a-Budget-Mono-Red-and-Boros-Burn/1de6e805-3ed3-450a-8677-e5395e07cd69/

https://infinite.tcgplayer.com/article/Competitive-MTG-Modern-on-a-Budget-Mono-Red-and-Boros-Burn/1de6e805-3ed3-450a-8677-e5395e07cd69/
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Mainboard
Four Eidolon of the Great Revel replacing four Viashino Pyromancer
Four Sunbaked Canyon replacing four Mountain
One Fiery Islet replacing one Mountain
Eidolon of the Great Revel is one of the most significant investments when it comes to building Burn, but it's also one of the biggest payoffs for the strategy. Modern is full of low-mana value cards all of which trigger Eidolon of the Great Revel. Also, the Enchantment Spirit always deals damage if the opponent fires off a removal spell, so it makes up for the lack of haste by guaranteeing the damage instead. The longer Eidolon of the Great Revel stays on the battlefield gives more consequences to the opponent, where in some cases, their own spell can kill them leaving them in an unwinnable situation.
Shifting into Modern Boros Burn
Mainboard
Four Arid Mesa replacing four Mountain
Two Sacred Foundry replacing two Mountain
Four Inspiring Vantage replacing four Ramunap Ruins
Two Lightning Helix replacing two Skullcrack
Four Boros Charm replacing four Searing Blood
Sideboard
Two Path to Exile replacing two Tormod's Crypt
Two Rest in Peace replacing two Tormod's Crypt
Three Sanctifier En-Vec replacing three Molten Rain
Arid Mesa should be your priority when optimizing into Boros Burn as this grabs both Mountain and Sacred Foundry while remaining kind to the wallet. Inspiring Vantage is one of the best lands in Boros Burn as it comes in untapped in the early turns, giving you access to cast Lightning Helix and Boros Burn on turn two or three. Once you have completed the mana base, you can add the white splash since you have enough sources to support it. Boros Charm is the only burn spell that deals more than three damage but comes with two other abilities worth keeping in mind. While you are going to use the first mode the most, giving your Monastery Swiftspear or Goblin Guide double strike for the kill can offer more damage than burning the opponent with the instant. Also, using Boros Charm for the indestructible ability is valid in the right circumstances. While you would rather deal damage with the spell, protecting your creatures from a board wipe or a land destruction spell can be relevant, giving you a lifeline as the game progresses. 


Optimal Modern Boros BurnTo round out the upgrades fully, adding a few more fetch lands gives you excellent filtering to ensure you draw into more action. 
Adding a couple of red-based fetches improves the probability of drawing into more action instead of flooding out on mana. If you happen to have more than three lands in play during a game, then it's considered flooding by Boros Burn's standards. Another reason why you see Sunbaked Canyon and Fiery Islet feature in these lists is you want to sacrifice these for card draw aggressively after hitting your third land drop. Scalding Tarn is the cheapest red-based fetch outside of Arid Mesa thanks to the Modern Horizons 2 reprint, making Boros Burn an extremely affordable Modern strategy even when optimized. You can opt for Bloodstained Mire or Wooded Foothills instead if you already have these in your collection, but they command a steep price due to seeing fewer reprints. If you are fearful of Pithing Needle effects, you can run a mix of the red-based fetches to circumvent this, but this is a minor detail that doesn't crop up often.
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On the affordability to power scale, Boros Burn is the best strategy to play in Modern. It's quick, explosive, and often becomes one of the better options to play in the format. In the current Modern metagame, Boros Burn can go under these slow Four-Color Yorion piles by being assertive, while also offering reasonable match-ups against Living End and Grixis Death's Shadow. Another benefit to playing Boros Burn is the strategy is low maintenance, the core rarely deviates or changes due to the cards already being so good at what they do. As a result, you can build the deck without worrying about buying new cards to keep up with trends or the latest sets.>>