With the release of Pokemon Scarlet & Violet, catching them all has never been harder. We now have over 1,000 Pokemon to enjoy, despise, or feel ambivalent towards, although some have received much more love from Game Freak than others over the years. Since it can't be expected for Game Freak to naturally cram masses of Pokemon into one single game, sacrifices have been made over the past few games, as several Pokemon have been cut. I don't think I need to remind you of the Dexit fiasco.
While Game Freak probably does its best to make sure everyone's favorite Pokemon is included in at least a few games, there are some that the developer seems to have forgotten about over the years. Whether that be because their designs are a bit pants or Game Freak itself doesn't like them very much, there are some Pokemon that are much harder to grab in more modern Pokemon titles simply because of how infrequently they appear. Pokemon fans have been discussing which of their favorites deserves to be more in the spotlight (thanks GamesRadar).
Redditor u/Shiny_Hypno kicks things off with Volbeat and Illumise, a pair of bug type Pokemon first introduced in Pokemon Ruby & Sapphire. Their designs are pretty cute and the move Signal Beam is no joke, but perhaps the reason they haven't been included much is because they don't evolve? It could also be a similar case with their backup choice too, as Furfrou's last appearance was in Pokemon Sun & Moon.
In fact, we might be onto something with the whole no evolution theory, as two more Pokemon fans - u/streetbyrd and u/Lifeguard446 - think that Game Freak is neglecting Kecleon and Castform respectively, both introduced in Pokemon Ruby & Sapphire and have unique gimmicks. Kecleon could only be found with a Devon Scope, while Castform changes it shape depending on the weather. They're pretty novel Pokemon and it's a shame we haven't seen more of either of them in modern titles.
However, there's a bunch of evolutionary lines that are also pretty much trapped in their debut games, the best example being Blitzle and Zebstrika. They were introduced in Black & White, as u/Thelexhibition complains about how difficult it is to grab them in modern titles. There's also the mysterious case of Ducklett and Swanna, brought up by u/DaveHalu. Considering it's a full-blown swan, it's exclusion from Britain-inspired Pokemon Sword & Shield makes you question what the poor thing has to do to get back in.
Of course, we can't talk about forgotten 'mons without talking about the scientifically proven, most unpopular Pokemon out there, and it is actually one that we don't see in many games. YouTuber Thomas Game Docs used Google analytics to figure out that Watchog from Pokemon Black & White is the least searched for Pokemon in the entire series, meaning it's not just Game Freak that forgot about it - you did too.