I never got to play Pokemon on handhelds as a kid, so my only experience is through emulators and romhacks as someone much older, so there’s no way to transfer Pokemon between games (that I know of).

So I just started naming mine by species, and treating it as if I just met a Pokemon I’d had before again in the wild. Different natures or IVs didn’t matter; aren’t YOU different over the course of your life?

Like “hey look, it’s Crockjock again!” if I wanted to do a run with Totodile. Same Pokemon, different adventure.

I’ve turned to ChatGPT. It actually does a pretty good job!

I have given every single Pokémon a nickname since red/blue, except the ones I was planning to trade (as the recieving player might not want a nickname and you can not actually un-do it). There is no fixed theme tho - sometimes they get boring everyday names (like Pascal and Francis) sometimes fantasy names from other franchises (my first ever Noibat was named Nazgûl for example, and my first Torterra was Great A’Tuin), sometimes IRL mythology (Fenrir the Houndoom) and sometimes IRL items/plants/creatures (like Rafflesia the Bulbasaur)

In Sword/Shield, wild 'mons could come with a “mark” that gave them an extra title, and I made a habit out of trying to find appropiate nicknames like “Decaf” for a Polteageist that came with the “sleepy” mark (this guy here)

The downside is that I sometimes had a hard time remembering what the Pokémon species was actually called. =P