I used a Python script to compare the X/Y regional dex and Legends: Z-A dex, sorting the Pokemon into buckets. The results are below.
In X/Y, but not in Legends: Z-A
Zigzagoon, Linoone, Caterpie, Metapod, Butterfree, Bidoof, Bibarel, Dunsparce, Azurill, Marill, Azumarill, Burmy, Wormadam, Mothim, Surskit, Masquerain, Corphish, Crawdaunt, Goldeen, Seaking, Psyduck, Golduck, Farfetch'd, Ledyba, Ledian, Combee, Vespiquen, Skitty, Delcatty, Doduo, Dodrio, Plusle, Minun, Gulpin, Swalot, Oddish, Gloom, Vileplume, Bellossom, Sentret, Furret, Nincada, Ninjask, Shedinja, Kecleon, Smeargle, Croagunk, Toxicroak, Ducklett, Swanna, Volbeat, Illumise, Hoppip, Skiploom, Jumpluff, Munchlax, Snorlax, Whismur, Loudred, Exploud, Zubat, Golbat, Crobat, Axew, Fraxure, Haxorus, Hoopa, Volcanion, Drifloon, Drifblim, Mienfoo, Mienshao, Zangoose, Seviper, Spoink, Grumpig, Lunatone, Solrock, Wingull, Pelipper, Taillow, Swellow, Dwebble, Crustle, Tentacool, Tentacruel, Wailmer, Wailord, Luvdisc, Shellder, Cloyster, Qwilfish, Horsea, Seadra, Kingdra, Relicanth, Rhyhorn, Rhydon, Rhyperior, Woobat, Swoobat, Cubone, Marowak, Ferroseed, Ferrothorn, Snubbull, Granbull, Yanma, Yanmega, Sigilyph, Golett, Golurk, Nosepass, Probopass, Makuhita, Hariyama, Throh, Sawk, Starly, Staravia, Staraptor, Stunky, Skuntank, Nidoran♀, Nidorina, Nidoqueen, Nidoran♂, Nidorino, Nidoking, Chingling, Chimecho, Mime Jr., Mr. Mime, Solosis, Duosion, Reuniclus, Wynaut, Wobbuffet, Roggenrola, Boldore, Gigalith, Tauros, Miltank, Pachirisu, Exeggcute, Exeggutor, Chatot, Mantyke, Mantine, Clamperl, Huntail, Gorebyss, Remoraid, Octillery, Corsola, Chinchou, Lanturn, Alomomola, Lapras, Articuno, Zapdos, Moltres, Diglett, Dugtrio, Trapinch, Vibrava, Flygon, Geodude, Graveler, Golem, Slugma, Magcargo, Shuckle, Skorupi, Drapion, Wooper, Quagsire, Karrablast, Escavalier, Shelmet, Accelgor, Carnivine, Poliwag, Poliwhirl, Poliwrath, Politoed, Barboach, Whiscash, Purrloin, Liepard, Poochyena, Mightyena, Pawniard, Bisharp, Murkrow, Honchkrow, Foongus, Amoonguss, Lotad, Lombre, Ludicolo, Buizel, Floatzel, Basculin, Rotom, Magnemite, Magneton, Magnezone, Voltorb, Electrode, Swinub, Piloswine, Mamoswine, Cubchoo, Beartic, Smoochum, Jynx, Sneasel, Weavile, Timburr, Gurdurr, Conkeldurr, Torkoal, Sandshrew, Sandslash, Heatmor, Durant, Spearow, Fearow, Cryogonal, Gligar, Gliscor, Hoothoot, Noctowl, Igglybuff, Jigglypuff, Wigglytuff, Zorua, Zoroark, Gothita, Gothorita, Gothitelle, Bonsly, Sudowoodo, Spinda, Teddiursa, Ursaring, Lickitung, Lickilicky, Ditto, Druddigon, Deino, Zweilous, Hydreigon (total: 254)
In Legends: Z-A, but not in X/Y
Chikorita, Bayleef, Meganium, Tepig, Pignite, Emboar, Totodile, Croconaw, Feraligatr, Cleffa, Clefairy, Clefable, Buneary, Lopunny, Numel, Camerupt, Drilbur, Excadrill, Tynamo, Eelektrik, Eelektross, Snorunt, Glalie, Froslass, Falinks, Drampa, Beldum, Metang, Metagross (total: 29)
