Steeds with Useful Abilities
These pokemon all have 600 BST, thus would almost always be Steeds
There are several other Steeds that can be well-utilized for typing, movepool, and stats, but have less useful abilities such as Pressure
:Mew: Psychic, Synchronize (used for movepool more than ability)
:Victini: Psychic, Victory Star
:Cresselia: Psychic, Levitate
:Latias:/:Latios: Dragon, Levitate
:Hydreigon: Dark, Levitate
:Dragapult: Dragon, Clear Body
:Kommo-o: Dragon, Bulletproof
:Salamence: Dragon, Intimidate
:Genesect: Bug, Download
:Volcanion: Fire, Water Absorb
:Heatran: Fire, Flash Fire
:Jirachi: Steel, Serene Grace
:Magearna: Steel, Soul Heart
:Metagross: Steel, Clear Body
:Landorus-Therian: Ground, Intimidate
:Tyranitar: Rock, Sand Stream
:Zeraora: Electric, Volt Absorb
:Goodra: Dragon, Sap Sipper
Steeds/Riders with Useful Abilities
These pokemon have 580-570 BST, so they can easily be either Riders or Steeds
There are several others that can be utilized for typing, movepool, or stats, but have less useful abilities
:Tornadus-Therian: Flying, Regenerator
:Tornadus: Flying, Prankster
:Thundurus: Electric, Prankster
:Thundurus-Therian: Electric, Volt Absorb
:Azelf:/:Uxie: Psychic, Levitate
:Articuno-Galar: Psychic, Competitive
:Zapdos-Galar: Fighting, Defiant
:Blacephalon: Fire, Beast Boost
:Buzzwole:/:Pheromosa: Bug, Beast Boost
:Celesteela: Steel, Beast Boost
:Kartana: Grass, Beast Boost
:Nihilego:/:Stakataka: Rock, Beast Boost
:Xurkitree: Electric, Beast Boost
:Guzzlord: Dark, Beast Boost
:Tapu Bulu: Grass, Grassy Surge
:Tapu Lele: Psychic, Psychic Surge
:Tapu Koko: Electric, Electric Surge
:Tapu Fini: Water, Misty Surge
Riders that provide an offensive boost (some of these can be Steeds)
:Porygon-Z: Normal, Adaptability
:Urshifu:/:Urshifu-Rapid Strike: Fighting, Unseen Fist
:Naganadel: Poison, Beast Boost
:Toxtricity: Electric, Punk Rock
:Copperajah: Steel, Sheer Force
:Darmanitan: Fire, Sheer Force
:Barbaracle:/:Lycanroc-Dusk: Rock, Tough Claws
:Conkeldurr:/:Machamp:/:Throh: Fighting, Guts
:Aurorus: Rock, Refrigerate
:Malamar: Dark, Contrary
:Ninjask: Bug, Speed Boost
:Araquanid: Water, Water Bubble
:Wailord: Water, Water Veil
:Togekiss: Fairy, Hustle
:Corsola: Water, Hustle
:Doublade: Steel, No Guard
:Galvantula:/:Butterfree: Bug, Compound Eyes
:Tyrantrum: Rock, Strong Jaw
:Boltund: Electric, Strong Jaw
:Drednaw: Water, Strong Jaw
:Dhelmise: Ghost, Steelworker
:Zoroark: Dark, Illusion
:Bisharp: Dark, Defiant
:Raichu-Alola: Electric, Surge Surfer
:Dunsparce: Normal, Serene Grace
Riders that offer defensive or supportive abilities (some can be Steeds)
:Arcanine: Fire, Intimidate
:Gyarados: Water, Intimidate
:Krookodile: Ground, Intimidate
:Stoutland:/:Tauros: Normal, Intimidate
:Hitmontop: Fighting, Intimidate
:Persian-Alola: Dark, Fur Coat
:Bewear:/:Dubwool: Normal, Fluffy
:Blissey: Normal, Natural Cure
:Roserade: Grass, Natural Cure
:Altaria: Dragon, Natural Cure
:Trevenant: Ghost, Natural Cure
:Ferrothorn: Grass, Iron Barbs
:Druddigon: Dragon, Rough Skin
:Sharpedo: Water, Rough Skin
:Volcarona: Bug, Flame Body
:Magmortar:/:Talonflame: Fire, Flame Body
:Electabuzz:/:Raichu:/:Manectric:/:Emolga: Electric, Static
:Stunfisk: Ground, Static
:Grimmsnarl: Dark, Prankster
:Whimsicott: Grass, Prankster
:Klefki: Steel, Prankster
:Salazzle: Poison, Corrosion
:Magnezone: Electric, Magnet Pull
Riders that provide immunity (some of these can be Steeds)
:Rotom: Electric, Levitate
:Flygon: Ground, Levitate
:Cryogonal: Ice, Levitate
:Bronzong: Steel, Levitate
:Claydol: Ground, Levitate
:Vikavolt: Bug, Levitate
:Weezing:/:Weezing-Galar: Poison, Levitate
:Lunatone:/:Solrock: Rock, Levitate
:Haunter: Ghost, Levitate
:Lapras:/:Vaporeon:/:Poliwrath::Politoed:/:Dracovish:/:Arctovish:/:Jellicent: Water, Water Absorb
:Heliolisk: Electric, Dry Skin
:Maractus: Grass, Water Absorb
:Jolteon:/:Dracozolt:/:Arctozolt: Electric, Volt Absorb
:Lanturn: Water, Volt Absorb
:Electivire: Electric, Motor Drive
:Pincurchin: Electric, Lightning Rod
:Centiskorch:/:Flareon:/:Ninetales: Fire, Flash Fire
:Chandelure: Ghost, Flash Fire
Riders that are primarily added for typing or movepool, but still offer an ability with situational use
:Milotic: Water, Marvel Scale
:Tentacruel: Water, Clear Body
:Toxapex: Poison, Merciless
:Shuckle:/:Crustle: Bug, Sturdy
:Aggron:/:Skarmory: Steel, Sturdy
:Gigalith: Rock, Sturdy
:Sawk: Fighting, Sturdy
:Gengar: Ghost, Cursed Body
:Froslass: Ice, Cursed Body
:Marowak-Alola: Fire, Cursed Body
:Cradily: Rock, Suction Cups
:Octillery: Water, Suction Cups
:Pangoro: Fighting, Iron Fist
:Golurk: Ground, Iron Fist
:Gastrodon: Water, Sticky Hold
:Slowbro:/:Slowking:/:Whiscash: Water, Oblivious
:Mamoswine:/:Jynx: Ice, Oblivious
:Eldegoss: Grass, Cotton Down
:Pyukumuku: Water, Innards Out
:Scrafty: Dark, Shed Skin
:Pupitar: Rock, Shed Skin
:Dragonair: Dragon, Shed Skin
:Aerodactyl:/:Onix:/:Sudowoodo: Rock, Rock Head
:Marowak:/:Rhydon: Ground, Rock Head
:Steelix: Steel, Rock Head
:Shelgon: Dragon, Rock Head