This does not include Megas or Primals, and generally most alternate forms.
Magikarp and Feebas: 20, 10, 15, 20, 55, 80; BST 200
Silcoon and Cascoon: Same stat numbers, in the same order (50, 35, 55, 25, 25, 15; BST 205)
Lotad and Seedot: 40, 40, 30, 30, 30, 50; BST 220
Zigzagoon and Galarian Zigzagoon have the same BST and same stats (38, 30, 41, 30, 41, 60; BST 240)
Noibat and Zubat: 40, 30, 35, 45, 40, 55; BST 245
Fomantis and Hoppip: 40, 55, 35, 50, 35, 35; BST 250
Ratatta and Alolan Ratatta have the same BST and same stats (30, 56, 35, 25, 35, 72)
Taillow and Wingull: 30, 30, 30, 40, 55, 85; BST 270
Vulpix and Alolan Vulpix have the same BST and same stats (38, 41, 40, 50, 65, 65; BST 299)
Geodude and Alolan Geodude have the same BST and same stats (40, 80, 100, 30, 30, 20; BST 300)
Snivy and Oshawott: 45, 45, 55, 45, 55, 63; BST 308
Charmander and Cyndaquil: Same stat numbers, in the same order (39, 52, 43, 60, 50, 65; BST 309)
Squirtle and Totodile: 44, 48, 65, 50, 64, 43; BST 314
Slowpoke and Galarian Slowpoke have the same BST and same stats (90, 65, 65, 40, 40, 15; BST 315)
Darumaka and Galarian Darumaka have the same BST and same stats (70, 90, 45, 15, 45, 50; BST 315)
Pansage, Pansear, and Panpour: Same stat numbers, in the same order (50, 53, 48, 53, 48, 64; BST 316)
Bulbasaur and Chikorita: 45, 49, 49, 65, 65, 45; BST 318
Grimer and Alolan Grimer have the same BST and same stats (80, 80, 50, 40, 50, 25; BST 325)
Vullaby and Morgrem: 70, 55, 75, 45, 65, 60; BST 370
Graveler and Alolan Graveler have the same BST and same stats (55, 95, 115, 45, 45, 35; BST 390)
Gloom and Porygon: 60, 65, 70, 85, 75, 40; BST 395)
Plusle and Minun: 60, 50, 40, 85, 75, 95; BST 405
Ivysaur and Bayleef: 60, 62, 63, 80, 80, 60; BST 405
Charmeleon and Quilava: Same stat numbers, in the same order (58, 64, 58, 80, 65, 80; BST 405)
Wartortle and Croconaw: 59, 63, 80, 65, 80, 58; BST 405
Ponyta and Galarian Ponyta have the same BST and same stats (50, 85, 55, 65, 65, 90; BST 410)
Servine and Dewott: 60, 60, 75, 60, 75, 83; BST 413
Wormadam Plant and Sandy: 60, 59, 85, 79, 105, 36; BST 424
Marowak and Alolan Marowak have the same BST and same stats (60, 80, 110, 50, 80, 45; BST 425)
Volbeat and Illumise: 65, 73, 75, 47, 85, 85; BST 430
Lunatone and Solrock: 90, 55, 65, 95, 85, 70; BST 460
Phione and Glalie: Same stat numbers, in the same order (80, 80, 80, 80, 80, 80; BST 480)
Darmanitan and Galarian Darmanitan have the same BST and same stats (105, 140, 55, 30, 55, 95; BST 480)
Cofagrigus and Runerigus: 58, 50, 145, 95, 105, 30; BST 483
Turtonator and Drampa: 60, 78, 135, 91, 85, 36; BST 485
Slowbro and Slowking: 95, 75, 100, 110, 80, 30; BST 490
Golem and Alolan Golem have the same BST and same stats (80, 120, 130, 55, 65, 45; BST 495)
Simisage, Simisear, Simipour: Same stat numbers, in the same order (75, 98, 63, 98, 63, 101; BST 498)
Rapidash and Galarian Rapidash have the same BST and same stats (65, 100, 70, 80, 80, 105; BST 500)
Muk and Alolan Muk have the same BST and same stats (105, 105, 75, 65, 100, 50; BST 500)
Dracozolt and Dracovish: 90, 100, 90, 80, 70, 75; BST 505
Arctozolt and Arctovish: 90, 100, 90, 90, 80, 55; BST 505
Gardevoir and Gallade: 68, 65, 65, 125, 115, 80; BST 518
All Rotom forms: 50, 65, 107, 105, 107, 86; BST 520
Vaporeon, Jolteon, Flareon, Espeon, Umbreon, Leafeon, Glaceon, Sylveon: 130, 65, 60, 110, 95, 65; BST 525
Venusaur and Meganium: 80, 82, 83, 100, 100, 80; BST 525
Blastoise and Feraligatr: 79, 83, 100, 85, 105, 78; BST 530
Charizard and Typhlosion: Same stat numbers, in the same order (78, 84, 78, 109, 85, 100; BST 534)
Gyarados and Milotic: 95, 125, 79, 60, 100, 81; BST 540
Tapu Koko, Tapu Lele, Tapu Bulu, Tapu Fini: 70, 115, 85, 95, 75, 130; BST: 570
Articuno, Zapdos, Moltres: 90, 90, 85, 125, 90, 100; BST: 580
Raikou, Entei, Suicune: 90, 85, 75, 115, 100, 115; BST: 580
Cobalion, Terrakion, Virizion, Keldeo: 91, 72, 90, 129, 90, 108; BST: 580
Tornadus Incarnate and Thundurus Incarnate: 79, 115, 70, 125, 80, 111; BST: 580
Regirock and Regice: 80, 100, 20050, 1000, 50; BST 580
Latias and Latios: 80, 80, 90, 110, 130, 110; BST: 600
Mew, Celebi, Jirachi, Manaphy, Shaymin, Victini: 100, 100, 100, 100, 100, 100; BST: 600
Zacian and Zamazenta: 92, 130, 115, 80, 115, 138; BST: 670
Kyogre and Groudon: 100, 100, 90, 150, 140, 90; BST: 670
Dialga, Palkia, Reshiram, and Zekrom: 100, 120, 120, 150, 100, 90; BST: 680
Solgaleo and Lunala: 137, 137, 107, 113, 89, 87; BST: 680
Xerneas and Yveltal: 126, 131, 95, 131, 98, 99; BST: 680
Lugia and Ho-oh: 106, 90, 130, 90, 154, 110; BST: 680
Source: Check Bulbapedia articles of each pair if you don't believe me.
Wow! That took a really long time! Hope I helped!