Syrix, Carrier of the Flame
This commander rewards you for having big Phoenix creatures in play and having any kind of creature leaving your graveyard. This phoenix tribal-theme deck looks to recur big and evasive creatures from the graveyard, doing direct damage to remove opponents' blockers, and swinging in combat with multiple big bodies that do not care for their own safety.
Combos & Strategies
Our Phoenix tribe has many of the same ability across its creatures, but not all of them trigger in the same capacity. While the majority will trigger on their own over the course of gameplay, others require a little more support:
Kuldotha Phoenix requires us to have 3+ artifacts in play, so we have leaned into some artifact lands to help increase that count: Darksteel Citadel, Drossforge Bridge, Great Furnace, & Vault of Whispers
Everquill Phoenix and Rekindling Phoenix both rely on the token card they create to be able to return from the graveyard
Aurora Phoenix and Screeching Phoenix will have to rely on other methods of recurring them, as will our changeling phoenixes Graveshifter and Taurean Mauler
Our remaining phoenixes should have no trouble returning under their own powers: Akoum Firebird, Ashcloud Phoenix, Firewing Phoenix, Flame-Wreathed Phoenix, Flamewake Phoenix, Immortal Phoenix, Lightning Phoenix, Phoenix of Ash, Shard Phoenix, Shivan Phoenix, Skarrgan Firebird, Skyfire Phoenix, Sunstreak Phoenix, and Warcry Phoenix.
For non-phoenixes, Burnished Hart and Solemn Simulacrum help provide ramp and are great reanimation targets for some of our spells. Homura, Human Ascendant returns to play as a large anthem when it dies which can help beef-up our entire board. Finally, Yidaro, Wandering Monster is a great inclusion as cycling the card causes it to then leave our graveyard and trigger Syrix, Carrier of the Flame, and in the late game becomes another large creature to swing at our opponents with.
We are running several anthem effects to make our creatures bigger and get more bang-for-our-buck with our commander's triggered abilities. Death Pit Offering, Door of Destinies, Ferocity of the Wilds, Homura, Human Ascendant, Heraldic Banner, Flowstone Surge, In the Web of War, and Obelisk of Urd all ensure our creatures are going to be a constant threat. Doubling effects in the form of Flameshadow Conjuring and Molten Echoes help us get more distance out of recurring a single phoenix.
Several of our creatures are going to return under their own power, but it is important not to rely on that always happening. Cards like Graveshifter, Living Death, Grave Upheaval, Corpse Dance, Feign Death, Phyrexian Reclamation, Tortured Existence, and Wake the Dead are excellent ways for us to recur any creature, and some of these can trigger during our opponent's turns, allowing for additional Syrix, Carrier of the Flame triggers. Whip of Erebos not only can recur a phoenix (albeit only once per creature) but gives all our creatures lifelink, which combined with their big bodies and other ETB triggers means we could gain a lot of life in even just a single turn.
Phoenixes are generally high in mana cost, and several of them require us to re-cast them from our hand or graveyard, so effects with lower their costs are VERY important. Herald's Horn, Ruby Medallion, and Urza's Incubator can help minimize our creature's costs (or you can use the more budget-friendly Hazoret's Monument and Heartless Summoning; I just happen to have had these cards in my collection). Black Market and Braid of Fire can help us generate more mana as the game goes on. Staples such as Arcane Signet, Expedition Map, and Rakdos Signet can help us fix our colors if needed. Heraldic Banner (choosing red) pulls double-duty as another anthem effect, while Liquimetal Torque can help make some permanents easier to destroy by turning them into artifacts. Grave Upheaval and Kazuul's Fury both have the option of becoming lands if we are short on mana early on. Molten Slagheap can help us build-up to a larger spell a few times as well.
Since we don't care about our creatures' safety, its important to get some value out of their deaths. Grave Pact lets us take advantage of our deck's self-sacrificing nature to thin out the ranks of our opponents' creatures, while Vampiric Rites, High Market, and Village Rites give us some sack outlets and pair well with Corpse Dance.
Of course we are going to include staple non-creature removal cards in our colors with Chaos Warp, Feed the Swarm, and Shattering Pulse. Our deck can generate large amounts of mana and having a spell with Buyback helps us focus that mana when its not needed for creature recursion. Kazuul's Fury and Warstorm Surge let us take advantage of our big creatures by doing some direct-damage with them. Hurl Through Hell is a versatile card that can remove an opponent's creature and let us re-cast it, or it can be used to save one of our creatures from a fate worse than death.
Finally, we have some high-value cards which work well with our strategies and themes:
Industrial Advancement can sacrifice one phoenix for another, letting us build our flock faster.
Sunbird's Invocation besides being thematic can help turn our high-mana-value casts into a second spell for free.
Vorpal Sword can be a late-game mana sink to close-out the game, and also combos with Shard Phoenix or Magma Phoenix to become a board wipe or with our commander to be able to snipe away our opponents' toughest creatures.
Alternatives, Substitutes, and Upgrades (the Maybeboard)
There are lots of cards which aid our theme which were not included as we've already got their effect covered in another way, the card was not budget-friendly (for cards I didn't already own), or it was just eventually cut when trimming down to deck-size. These are cards you might consider when adapting this deck as your own.
If your playgroup is okay with poison counters, Grafted Exoskeleton is great equipment upgrade for the Vorpal Sword
Butcher of Malakir and Dictate of Erebos make fine substitutions for Grave Pact
Hazoret's Monument can sub for Ruby Medallion as a more budget-friendly option
Heartless Summoning can sub for Urza's Incubator in that same capacity
Supernatural Stamina can sub for Feign Death
Helm of the Host, Minion Reflector, and Mirror March could replace Flameshadow Conjuring and/or Molten Echoes
Pandemonium, Terror of the Peaks, Flayer of the Hatebound, Where Ancients Tread, Outpost Siege, and Impact Tremors could substitute or compliment Warstorm Surge
Purphoros, God of the Forge could be an upgrade due to its ETB trigger, but also as a mana sink that pumps the power of your Phoenixes
Sneak Attack and Purphoros, Bronze-Blooded also make fine upgrades for cheap-playing of your Phoenixes, especially ones that return to your hand - however they don't work well with some of our cast-trigger cards like Sunbird's Invocation or Door of Destinies
Disturbed Burial is a budget alternative to Corpse Dance
Basilisk Collar fills a similar role as Vorpal Sword or Whip of Erebos
Fling is a slightly cheaper but less versatile Kazuul's Fury
Alternative sack-outlets include Altar of Dementia, Attrition, Goblin Bombardment, and Phyrexian Tower
Some upgraded anthem effects are Eldrazi Monument, Metallic Mimic, Mikaeus, the Unhallowed, and The Immortal Sun. War Horn could be included as a substitute anthem if you need more artifacts.
Thematically Beacon of Destruction, Beacon of Unrest, and Hammer of Bogardan play well with the recursion theme
Desecrated Tomb is an easy card to synergize with our commander, but many of our anthems don't deal with black creatures and/or non-phoenixes
Necromatic Selection or Decree of Pain make excellent board wipes if you need more
Persistent Specimen, Reassembling Skeleton, and Sanitarium Skeleton are all cheap recurring creatures if you need the deck to move faster
Sword of Hearth and Home and Sword of the Animist are good additional ramp options
Finally, if you need additional reanimating effects Writ of Return, Underworld Sentinel, Palace Siege, Kardur's Vicious Return, Doomed Necromancer, and Cauldron Dance are okay options
Excluded Phoenixes and Ways to Support Them
Not every phoenix works well in this deck, and we've excluded a few of them. If you want to flex these phoenixes into your deck, here are some support ideas.
Aurora Phoenix - This was actually kept in the deck due to its size, and Cascade letting us likely hit another creature or reanimation effect. There are not many Cascade cards which would support this card without overhauling themes, however Flamekin Herald is top of that support list.
Worldheart Phoenix - This creature's color identity is WUBRG and can't be included in a Syrix deck :-<
Bogardan Phoenix - The death counter effect means we can only recur this creature once normally. Effects that remove counters indiscriminately such as Aether Snap, Hex Parasite, Power Conduit, and Thrull Parasite could be used for additional support. Cards which bounce your own creatures, such as Erratic Portal would help this card as well, but none of these fit the rest of the deck's themes.
Firestorm Phoenix - An older card with a hefty mana cost and price tag, and a small body indicative of the older set's power level. It was cut for space.
Retriever Phoenix - Since the Learn mechanic only lets you discard a card to draw a card, it is lackluster in commander. On top of that, the phoenix is small in size. Some Learn cards which could support this phoenix better while supporting other phoenixes include: Academic Dispute, Enthusiastic Study, First Day of Class, Igneous Inspiration, and Poet's Quill
Spellpyre Phoenix - We have a few cycling cards in the deck, but not enough to reliably recur this phoenix. Its larger body made it a difficult cut, and it was ultimately cut mostly due to having cut spells that would help support this creature: Sanctuary Smasher, Solar Blast, Starstorm, Sweltering Suns, Tectonic Reformation, and Void Beckoner to call out the most impactful.
Arclight Phoenix and Chandra's Phoenix - More late cuts, these two are small bodied phoenixes that can be difficult to trigger their self-recur abilities since we are leaning more into a creature-heavy deck. The Chandra one especially requires that we use our spells to damage opponents, when we're more geared to destroy creatures with such spells. For both, running Chandra, Dressed to Kill is a must since she can help ramp and trigger both phoenixes. Spells with buyback such as Fanning the Flames or Searing Touch can also help trigger spell count for Arclight or direct-damage for Chandra. Earthquake can be a board wipe effect that assists these creatures as well.
Molten Firebird - Another small phoenix with a high mana cost. Its return to play ability is forced and causes you to skip your draw step. It is the color-shifted version of Ivory Gargoyle. If you're not setup with some extra ETB triggers, such as Warstorm Surge, the drawback can really slow you down, and opponents can target this creature to purposefully slow your deck. As such it has been cut in favor of other phoenixes.
Honorable Mention
Gravewaker should have been a phoenix IMHO and here's hoping WOTC prints a copy as a mono-black or hybrid-red-black phoenix creature in the future ;-)