So, wait, in the older Pokémon games... one could transfer in Pokémon from an even earlier version of the game that wasn’t available in that one?
So you could transfer in your Koffing from Poke-mans yellow (or whatever)?
Huh, I had no idea they had that kind of backwards compatibility.
My guess is someone went and said “hey we don’t have the time/money to animate every stupid Pokémon that’s ever been in a game with the fidelity needed for the Switch version”.
Correct. Here's how it worked:
Generation 1 (Red/Green/Blue/Yellow) -> Game Boy Link Cable connected to a second Game Boy ->
Generation 2 (Gold/Silver/Crystal)
<hard cutoff even though the hardware could have supported it>
Generation 3 (Ruby/Sapphire/Emerald/FireRed/LeafGreen) -> Pal Park (using the extra Game Boy Advance cartridge slot of the Nintendo DS) ->
Generation 4Generation 4 (Diamond/Pearl/Platinum/HeartGold/SoulSilver) -> Poké Transfer (using DS Download Play) ->
Generation 5Generation 5 (Black/White/Black 2/White 2) -> Pokémon Bank
Pokémon Bank ->
Generation 6 (X/Y/Omega Ruby/Alpha Sapphire) -> Pokémon Bank
Generation 1 (3DS Virtual Console) -> Pokémon Bank
Generation 2 (3DS Virtual Console) -> Pokémon Bank
Pokémon Bank ->
Generation 7 (Sun/Moon/UltraSun/UltraMoon) -> Pokémon Bank
Pokémon Bank -> Pokémon HOME
Pokémon GO -> Pokémon HOME
Let's Go Pikachu/Eevee -> Pokémon HOME
Pokémon HOME (limited selection) ->
Generation 8 (Sword/Shield) -> Pokémon HOME
Gold/Silver/Crystal remain the only games in the series that let you trade *back* a generation, but only if it was a Gen 1 Pokémon and didn't hold an item. All further generations were one-way only from older generation to newer generation. I should also note that two-way transferring with Bank is possible for Gens 6 and 7, and two-way transferring with HOME will be possible for Sword/Shield (but not GO or Let's Go, which are one-way.)
Theoretically, someone playing UltraSun could have been battling with Pokemon originally caught in 2002.
It's all been beautiful but clearly a lot of effort, which I've always commended Gamefreak for... With Gen 8 they decided it's suddenly too much and that's highly disappointing for me and a lot of others who have been diligently transferring forward every generation for 15+ years. Sure, they're "around" in Bank/Home, but what's the point of a Pokemon if it's stuck in the box all the time?