Here is a list of the unobtainable Pokemon through Gen 8:
Articuno, Zapdos, Moltres, Mew, Raikou, Entei, Suicune, Lugia, Ho-Oh, Celebi, Jirachi, Deoxys, Uxie, Mesprit, Azelf, Dialga, Palkia, Giratina, Heatran, Cresselia, Phione, Manaphy, Darkrai, Shaymin, Arceus, Victini, Cobalion, Terrakion...