3rd Generation Buddy Pokemon
The buddy System was one of the many concepts added to Pokemon GO that wasn't originally ever suppose to be. niantic, the developers of Pokemon GO, listened to the feedback that players had about how long it took to evolve certain Pokemon, later designing the buddy system so players could earn candy for a Pokemon that had only caught once. This would then allow a player, after walking enough, to fully evolve any Pokemon they'd like. Because of the Buddy System, if you've at least caught the 1st Stage evolution of a Pokemon Chain, you essentially have a way to obtain the remaining Pokemon of said Evolution Chain.
3rd generation buddy Pokemon Distance rewards
3rd generation Pokemon - 1km Per Candy buddy Reward:
poochyena, mightyena, zigzagoon, linoone, wurmple, silcoon, beautifly, cascoon, dustox, taillow, swellow, surskit, masquerain, whismur, loudred, exploud, aron, lairon, aggron, gulpin, swalot, wailmer, wailord, spoink, grumpig, swablu, altaria, barboach, whiscash
3rd generation Pokemon - 3km Per Candy buddy Reward:
treecko, grovyle, sceptile, torchic, combusken, blaziken, mudkip, marshtomp, swampert, lotad, lombre, ludicolo, seedot, nuzleaf, shiftry, wingull, pelipper, shroomish, breloom, makuhita, hariyama, azurill, nosepass, skitty, delcatty, meditite, medicham, electrike, Manetric, Plusle, Minun, Volbeat, Illumise, Roselia, Carvanha, Sharpedo, Numel, Camerupt, Torkoal, Spinda, Cacnea, Cacturne, Zangoose, Seviper, Lunatone, Solrock, Corphish, Cradaunt, Baltoy, Claydol, Lileep, Cradily, Anorith, Armaldo, Shuppet, Banette, Duskull, Dusclops, Wynaut, Snorunt, Glalie, Spheal, Sealeo, Walrein, Clamperl, Huntail, Gorebyss, Luvdisc
3rd generation Pokemon - 5km Per Candy buddy Reward:
ralts, kirlia, gardevoir, slakoth, vigoroth, slaking, nincada, ninjask, shedinja, sableye, mawile, trapinch, vibrava, flygon, feebas, milotic, castform, kecleon, tropius, chimecho, absol, relicanth, Bagon, Shelgon, Salamence, Beldum, Metang, Metagross
3rd generation Pokemon - 20km Per Candy buddy Reward:
regirock, regice, registeel, latias, latios, kyogre, groudon, rayquaza, jirachi, deoxys