So I've played pokemon handheld cartridge games for over 20 years. Mostly by watching/playing other people's, since the first and o lyrics one I ever got to own, on the only system I owned before adulthood, was sapphire on the GBA. I only recently learned what pseudo legendaries were, and I'm still learning alot. I am about to run through every handheld cart game for the first full playthrough, and I wanna know a few things.

What are each cart pseudo legendaries? (Yes this one is easy to find. I am just asking the community hoping to ref it all and such in one place.

I've heard about a "rare pokemon" in every game, where you basically can only see it once? (NOT LEGENDARIES) or super rare? In each cartridge apparently they exist? Or is this a complete misnomer?

Differences between edition cartridges, like r/b, g/s, etc. You just have to trade pokemon?

If I wanted to try to do this pure, and move pokemon from r/b, all the way up to the newest games, is that still possible?

I'm sorry, I know I'm asking a lot of questions. But I appreciate any help.