The lone MtG-related FB group I frequent has me theorycrafting this deck, because that is what browsing that page often results in my doing. The initial request was for a commander deck that is specifically good against Dragons. While some will argue that building a deck expressly to defeat another deck is bad Magic, I see it as no different than sideboarding in 60-card competitive formats.
Anyhow, my suggestion was Rashida Scalebane. As it happens, the best anti-dragon cards are mostly white, and mostly affordable.
That said, a deep collection, deep pockets, or a deep-seated hatred for a dragon deck makes all suggested cards possible.
Being from Mirage, her templating is different. Her errata is important, though, so here it is:
Legendary Creature — Human Soldier
{T}: Destroy target attacking or blocking Dragon. It can’t be regenerated. You gain life equal to its power.
The big takeaway being that she is part of two relevant tribes that have lots of support, so the deck might be able to leverage that. Otherwise, her ability is just clarified and templated to match current card wording.
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What do dragon decks have in common?
Dragon decks contain Red, because the vast majority of playable dragons are at least partially Red.
Dragon decks most often win through damage, be it EtB, combat, Dragon's Approach, or some combination of the three.
Most playable dragons fly, have power of 4 or greater, and cmc of 5+.
Now we know what to expect, and knowing is half the battle!
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In addition to Baneslayer Angel, white has two other creatures that inherently have Protection from Dragons: Dragon Hunter and Dragonstalker. These are your options for specifically anti-dragon cards.
Protection from Creatures gives us Commander Eesha and maybe Riders of Gavony, depending on final deck build. There is also Serra's Emissary, who can save you from creatures.
I'll address Protection from Red later.
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To keep this deck firmly in jank territory, Hundred-Handed One may be an awesome inclusion, once made monstrous and the correct Aura or Equipment is placed on it.
The trick is to find the correct Aura or Equipment.
Spirit Mantle, Unquestioned Authority, and Holy Mantle help with the blocking, while Gift of Immortality keeps him around. Darksteel Plate is a more versatile option.
Swords of Red and other colors provide both protection and evasion. Fire and Ice, Sinew and Steel, War and Peace. Plus, Sun Titan can bring them back from the graveyard.
Crown of Awe and Mask of Law and Grace are pretty focused jank.
Armored Ascension should be considered for every monowhite deck, although it is best on a double striker.
We also have the awesome art and one-time option of Spare from Evil, with its implied world of humans not being evil.
One thing all these cards have in common is that they allow you to go on the offensive quickly.
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White has a rather unique card ability in Magic, the ability that lets the caster name a card, and then that card cannot be cast or played.
Naming an opposing commander is simple. Play against any given deck a few times, and you learn which other key cards need to be named.
Gideon's Intervention, Nevermore, Null Chamber (group hug?), Voidstone Gargoyle - each of these can shut a commander out of play. Given that most Dragon decks cannot handle enchantments makes three-quarters of these permanently awesome.
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Mass Land Destruction. This polarizing strategy is an option, and one that White excels at - even moreso than Red. It's bad reputation stems from players dropping an Armageddon and not being able to follow up with a win a turn or two later. When used to seal the deal, MLD is just another tool for the victory-minded player's toolkit.
In addition to Armageddon, you have its functional reprint Ravages of War, the modal Catastrophe, the enchantment Fall of the Thran, and the related Cataclysm.
All that MLD can be self-crippling, barring Teferi's Protection or Terra Eternal - but this one tips your hand. Sun Titan and Crucible of Worlds allow for a consistent, slow rebuilding, and Planar Birth is an ideal recovery for your monowhite deck, but awful in the face of a monored Dragons build.
Just have a plan before taking the nuclear option.
MLD is suggested because Dragons tend towards 5+cmc, so undercutting land is an option. That said, Treasure tokens are a very real counter to land, and fittingly, several dragons create such tokens, getting around the threat of MLD. In addition to Treasures, there are also all the mana rocks that will need to be handled. I'll address direct removal later.
Stax is almost as contentious as MLD, but it works. White excels at Stax, and what White cannot do, artifacts can.
Dragons (and Treasure tokens) need to be untapped to be useful. Stax can hamper that.
Blind Obedience, Loxodon Gatekeeper, Kill Switch, Kismet, Authority of the Consuls, Imposing Sovereign, Kinjalli's Sunwing, Thalia, Heretic Cathar.
Stax can also just shut things off. Humility, Null Rod, Stony Silence, Torpor Orb, Hushbringer, Hushwing Gryff, Tocatli Honor Guard, and Karn, the Great Creator just stop different aspects of the game. Just be aware that your tricks are shut down, as well.
A note about Humility - Overwhelming Splendor is a terrible replacement. I understand making it a curse, but 8 cmc? It's probably good alongside Bitterheart Witch and/or Curse of Misfortunes, but on its own... yech! Is 5-color curses a thing?
The final part of Stax is just making combat or spells cost more or have upkeeps. Kataki, War's Wage hits both of you, but you're theoretically ready for it.
Reidane, God of the Worthy; Archon of Absolution; Ghostly Prison; Windborn Muse; Smothering Tithe; Aura of Silence; Archangel of Tithes; Spelltithe Enforcer; Tithe Taker; Baird, Steward of Argive; Esper Sentinel; Norn's Annex. Frankly, there may be more I missed, but this should provide a solid start.
Dragons can't do anything if they can't do anything, as it were.
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Given that most Dragon decks win through red-based damage, WW is a small price to pay to ensure your opponent hurts as much as you do. Poetic
Justice, if you will. Plus, you've got that sweet
Ruth Thompson art of a buff elf.
Celestial Purge may not seem like much on the surface, but exiling a
permanent at instant speed opens up all sorts of defensive opportunities. It makes
Devout Decree pale in comparison.
Lightwielder Paladin, though, has the potential to ruin a Dragon player, given time and presuming it gets through.
Southern Paladin might be useful, presuming you get to untap with it. Luckily, White has lots of ways to untap its team, or at least parts of it.
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Teferi's Protection, Flawless Maneuver, Angel's Grace, Luminesce, Samite Ministration, Timely Ward, Bastion Protector, Brave the Elements, Make a Stand, Unbreakable Formation, Selfless Spirit, and Your Temple is Under Attack can all save you and/or your team from whatever nonsense the Dragon player may try.
Grand Abolisher and Myrel, Shield of Argive both keep the Dragon player honest and only doing things on their turn.
Alongside Lightning Greaves and Swiftfoot Boots are the auras and equipment mentioned in other sections that double as protection.
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Austere Command, Cleansing Nova, Farewell, Slash the Ranks, Slaughter the Strong, Wrath of God, Martial Coup, and Mass Calcify all sweep the field of various things. Farewell is best, though.
Path to Exile, Generous Gift, Swords to Plowshares, Erase, Fate Forgotten, Forsake the Worldly, Crush Contraband - these are the targeted removal to first consider.
In all cases, exiling is the best policy, but sometimes destroying is all you can do.
If you need more targeted removal, White has several cards that aim at creatures with 4 or greater power, which is most playable dragons. Collective Effort, Guiding Bolt, Intrepid Hero, Radiant's Judgment, Reprisal, Retribution of the Meek, The Wanderer, Valorous Stance, and Elspeth, Sun's Champion look to be the most useful and/or versatile.
Take advantage of White's ability to take out enchantments and artifacts, because Dragon decks, especially Dragon decks containing Green and/or Blue, lean on enchantments for draw and EtB nonsense.
Equipoise provides an interesting option. Phasing out means phasing back in on the opponent's turn, so all you are doing is delaying the inevitable, unless you also have Disciple of Caelus Nin in play (if you could somehow flash in Disciple while an opponent is hiding behind Teferi's Protection, that would be hysterical!).
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People often call White the weakest color in Commander. Those people are wrong. That said, the solutions are rarely budget choices.
Land Tax + Scroll Rack and Smothering Tithe are the darlings of the higher-budget decks containing white, but there are other options.
Pearl Medallion, Archaeomancer's Map, Boreas Charger, Cartographer's Hawk, Keeper of the Accord, Knight of the White Orchid, Scouting Hawk, Loyal Warhound, Kor Cartographer, Gift of Estates, Tithe. Most of the White options require an opponent to have more land than you, though.
Endless Horizons is a two-edged card. The upside is how it clears lands from the deck, ensuring you draw gas the rest of the game while still making steady land drops. The downside is how an opponent's destroying it keeps those Plains away for the rest of the game. I have been assured IN ALL CAPS that this is NOT a form of ramp - so now you know, too.
Endless Atlas is a boon to any monocolor deck, but mostly White and Red.
Enlightened Tutor can fetch them all, and many of your various stax pieces, as well.
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This is monowhite, so of course there is a
Sun Titan. What all is Sun Titan returning to play, though?
Commander's Sphere,
Aura of Silence,
Children of Korlis,
Expedition Map,
Mind Stone,
Myriad Landscape,
any cycled lands, plus lots more mentioned throughout this post.
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Finishers. At some point, a deck needs to win.
Akroma's Will. True Conviction. Serra's Emissary - naming creatures. Bond of Discipline. All of these options demand you already have some creatures on the board.
Felidar Sovereign is its own wincon, but is not the intended route to victory here.
Approach of the Second Sun may prove to be the best choice, provided you stall long enough to cast it twice!
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Plains. 24-28 (or more) and whichever nonbasics you enjoy. I'd consider these ones, though.
Emeria, Sky Ruin. Flagstones of Trokair. Maze of Ith. Myriad Landscape. War Room. Glacial Chasm. Strip Mine.
Nonbasics suggest Expedition Map, and they wouldn't be wrong. Sun Titan lets you keep reusing the Map. Sun Titan can also help you reuse lands in the graveyard, like Myriad Landscape.
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Coming full circle, several of the presented options are Humans and/or Soldiers. I don't think there are enough to justify most tribal cards, though. Don't get me wrong, there are some neat cards that care about Humans in mono-white, and more neat cards that care about Soldiers, but they dilute the anti-dragon theme.
There are LOTS of cards that make Soldier tokens, so I have more cards to acquire for my Linden deck.
But it turns out that tribal is accidental, not on purpose with Rashida Scalebane.
Overall, an anti-dragon deck is a showcase of the best White offers alongside some niche and jank foolishness.