Take note that these are not obtainable via gameplay for now. They are basically Event mons.
Bulbasaur and Squirtle line are still in as well as Alola Starters. Sadly, that seems to be it for starters.
Mewtwo is also there because of course. Mythicals Celebi, Jirachi, Keldeo, Marshadow, Zeraora, and Meltan/Melmetal. Mew is obtainable via Pokeball Plus.
Gen 5 Sword of Justice trio and Kyurem/Zekrom as well as their fusions with Kyurem, for some reason, are in the code. Cosmog, Cosmeon, Solgaleo, Lunala, and Necrozma and its fusions except Ultra Necrozma are in the code.
Spoiler: In regards to the Gen 8 Mythicals (click to see content)
There are none lol.