- "Gotta catch 'em all!" was the catchphrase of the franchise, up until the Generation III games on the Game Boy Advance. There were multiple reasons the phrase was pulled; Gen III games were incompatible with the first two generations, not all Gen III Pokémon were even available in the original releases, and it only served as additional ammo for One Game for the Price of Two criticism. Plus, while getting 151 or even 251 Pokémon isn't too much of a stretch, especially when you can build your collection off previous games. But having to start from scratch to get 386 Pokémon spread out across seven games and two consoles, with several being unobtainable if you can't attend real-life events? Time to retire that slogan. The slogan returned to use in marketing by Gen VI, albeit not to its former prominence, as the games themselves had by then placed far greater emphasis on story than Pokémon collection. The worst example had to be Pokémon Sword and Shield, in which less than half the existent Pokémon were actually implemented. So it's literally impossible to collect them all even with hacking.
- Regions being referred to as "regions" made sense when the series was based on different Japanese provinces, suggesting that the regions are a part of a bigger country, implied by Johto continuing from the route numbers of Kanto. But ever since Pokémon Black and White introduced the first region not based on a Japanese province (Unova), it became clear that not all "regions" were in the same country. And ever since the introduction of the Kalos region (based on France) in Pokémon X and Y, regions have become more akin to countries (and are referred to as such, at least in the English translations).
- Similarly, the name of the National Dex made sense in the first four generations when the regions were based on Japan and were implied to be part of the same nation. But from the fifth generation onward, they've been based on random places from all over the world, and were implied to match the locations of their real world counterparts, making them most certainly not part of the same nation.
- The name of the Earth Badge in the Kanto Pokémon games. It was called that because the one who gave it out (Giovanni, in RGBYFRLG) used Ground-type Pokémon. But by GSCHGSS, he had been replaced by Blue, who uses a more diverse, multi-type team. This was averted in the Japanese versions, in which the badge is called Green Badge and actually becomes more fitting, since Blue is named ''Green'' there.
- It's traditional for there to be a series of checkpoints just before Victory Road, the last dungeon that has to be traversed before reaching the Elite Four, with each consecutively checking for all eight badges that will make you eligible for the Pokémon League. In the original games, your trek through the region essentially was a big circle, with the entrance gate to Victory Road being just outside the second town, which had the final Gym. As such, the checkpoints existed to emphasize that you really shouldn't be there yet. In contrast, the next four generations, not only had Victory Road be reasonably far from your starting point, but you couldn't even reach the gate until after you have eight badges anyway; there's usually some obstacle that requires the game's final Hidden Machine move, which is activated by the final gym badge, making the checks a mere formality.note Averted from Pokémon X and Y onwards. X and Y have the gate to Victory Road after the first major city, Pokémon Sun and Moon has its equivalent (Mount Lanakila) under construction for most of the game and doesn't bother with a checknote , and Pokémon Sword and Shield doesn't have one at all.
- Hidden Machine moves being impossible to forget (at least without consulting a Move Deleter NPC from Gen II on) is a Scrappy Mechanic that persisted because in Generation I and II, it was possible to leave a HM in your PC, making it theoretically possible to render the game Unwinnable by Mistake if you forgot an HM move and found yourself trapped in an area that required said move. In Generation III, the expansion of your bag meant that you'd always have the needed HMs on hand and could relearn a move if necessary, rendering the issue moot; however, you can still only delete HM moves with the help of a Move Deleter.note This naturally stopped being an issue when HMs stopped being a mechanic in Gen VII, with the field move functions now being found on Ride Pokémon, who can be summoned anytime, anywhere as needed, and are granted to you as part of the plot, leaving your party Pokémon to just fight. As a matter of fact, former field moves can't even be used the way they were in previous games since the game does not provide the option, not even non-HM moves like Sweet Scent. While some of the better HM attacks were converted to standard TMs (a fact lampshaded by several NPCs), most weren't, leaving Kartana (an Ultra Beast) in the amusing position of being the only thing able to learn Cut.
- Along these lines, the reason why HMs and TMs were originally distinguished is that TMs were only learnable once and then discarded, and could also be sold, both because of limited bag space. Selling TMs you didn't use was often a good way of making extra cash quickly. This persisted until Gen V, where they were changed to have unlimited use and couldn't be sold anymore, meaning the sole difference now was that HMs were required outside of battle to get past certain obstacles in the game.note Sword and Shield would introduce a new limited use item in Technical Records (TRs), with the additional advantage being that if you erase the move in any normal fashion, it can be relearned by that same Pokémon through the Move Reminder.
- In Gold and Silver, one of the 10 phone numbers you can have at a time is Bill's, who tells you how many spaces are left in your current Pokémon storage box and will also call to alert you when your current box is full. This is useful because you had to manually change boxes in the first two generations or else you couldn't capture another Pokémon. However, starting in Gen III, this was performed automatically, making registering Bill's number in the Gen IV remakes largely pointless (he instead tells you the number of spaces left in all of your boxes in total, in which case you are SOL if you manage to fill all of them). A downplayed example, you can register all the numbers you want in the remakes, so he's not hampering you, either.
- Lampshaded in Indigo Plateau in HeartGold and SoulSilver. In the original games, there was a nice Old Man who would have his Abra teleport you home. Since you couldn't fly between Kanto and Johto in those games, your only other way back until beating the Elite Four was slowly walking back. In the remakes, you can now use Fly to return to Johto from not only the Pokémon League, but also the reception gate building where the Old Man is located. As such, the remakes have the Old Man there to offer his services... only to note that because of Fly, most trainers turn him down. In fact, the game doesn't even let you take him up on his offer, not offering a Yes/No choice after he's finished talking.
- Dive Balls, introduced in Ruby and Sapphire, originally worked better on underwater Pokémon, but the Hoenn games are the only installments wherein you can dive underwater to encounter Pokémon. They were changed to also work better on wild Pokémon found while fishing or surfing. Amusingly, the attempts to make the Dive Ball remain relevant ended up passing this status onto the Lure Ball in the G/S/C remakes, which applied the same multiplier bonus, but only does so while fishing; meaning it also had to be changed, getting an even better multiplier bonus of x5 in Gen VI.
- The physical/special split did this to a number of Pokémon movesets. Prior to Gen IV, entire types were either physical (Normal, Fighting, Flying, Ground, Rock, Bug, Ghost, Poison, and Steel) or special (Water, Grass, Fire, Ice, Electric, Psychic, Dragon, and Dark). Thanks to the split, you now had Pokémon with moves that would have been amazing on them back in the day, but that they were now unable to truly capitalize on. While a fair number of Pokémon got some moveset changes to account for this, others didn't; for example, Aerodactyl and Gyarados both learn Hyper Beam via level-up. Prior to the split, it was a powerful physical attack on two fantastic physical attackers. After the split, it is now a powerful special attack inexplicably learned by two Pokémon that have barely passable special attack stats.note
- The Move Deleter NPC became this in Gen VII. The only reason you ever needed the Move Deleter mechanic (outside of certain gimmicky movesets that require a reduced number of moves) was to get rid of a Pokémon's HM moves, but since Sun and Moon removed HMs in favor of Ride Pokémon, it made the Move Deleter completely obsolete. Despite that, a Move Deleter still exists within Hau'oli City's Pokémon Center, even though you'll never require his services.
- The Pokémon cries from each past generation become this. Gaming technology has come a long way since even the Game Boy Color, and each Pokémon from Gens I and II still sound just like their original 8-bit counterparts. Some of the Spin-Off games, such as Pokémon Stadium, redid the old cries in better audio quality, but this wasn't fully carried over to the main series until Pokémon X and Y. Also, while a few Pokémon are meant to engage in Pokémon Speak like in the anime, limitations of the Game Boy system (they had to go through Development Hell to get Pikachu's voice in Yellow) prevented this, and afterwards it simply became a logistics issue.note As of Pokémon Sword and Shield, the only Pokémon to use Pokémon are Pikachu (from X and Y onwards, Eevee (from Pokémon Let's Go, Pikachu! and Let's Go, Eevee! onwards) and a Kantonian Meowth (in Sword and Shield, and only when Gigantamaxing). Other Pokémon that lack this are the Pokémon card game (obviously), Pokémon Adventures, Pokkén Tournament, and some of the Truer to the Text anime specials (such as Pokémon Generations and Pokémon: Twilight Wings).
- Nidoran is the only Pokémon whose male and female versions are considered separate species, but given the same name (aside from the gender marker). In Gen I, the gender trait did not exist, and thus the male and female Nidoran were classified as different creatures altogether, with their own bios and everything. With the introduction of genders and breeding in Gen II, male and female Pokémon of the same species have since been classified together as part of the same family even if they have different appearances as a result of sexual dimorphism (such as Jellicent) or divergent/stone-based evolution (Burmy having Wormadam and Mothim as an example of the former, Kirlia having Gardevoir and Gallade as an example of the latternote ); the divergent evolutions are still considered separate Pokémon, however. But Nidoran♂ and Nidoran♀ remain completely differentiated, mainly because combining them would screw up the number count. And though they actually have different names and were introduced after breeding was introduced, Volbeat and Illumise are in the exact same boat.
- It's made even more jarring by the fact that a Nidoran♀ inexplicably becomes sterile upon maturing into a Nidorina, apparently originating from an oversight in Generation II. More than fifteen years since the breeding mechanic was introduced in the Pokemon games and Game Freak still has yet to fix that problem with no official explanation as to why this is still the case. Pokémenopause?
- In Gen I, it's mentioned in the Pokémon Mansion journals that Mewtwo was born directly from Mew like a mammal, as opposed to hatching from an egg. It's mainly a case of Early Installment Weirdness, as this was prior to Gen II introducing breeding as a mechanic and establishing eggs to be the sole reproductive method for Pokémon. However, the FireRed/LeafGreen remakes don't change the journals to accommodate the shift. It would finally be amended in Pokémon Let's Go, Pikachu! and Let's Go, Eevee!, with the entry changed to simply say they "obtained a new Pokémon from Mew."
- The way some old Pokémon evolve, for better or for worse, can come off odd given the weird gimmicks that latter Pokémon make use of in order to evolve. For example, Gen IV's Mantyke can only evolve if a Remoraid is in the party (matching the lore of the creature), yet a similar situation isn't required to obtain Gen I's Slowbro, despite it being well-known in the lore that Slowpokes evolve only when a Shellder bites their tail.
- Stunfisk, a Ground/Electric Pokémon, can have the Limber ability, which protects it from paralysis. This was introduced before Electric-types were buffed to be immune to all sources of paralysis, making the ability completely useless most of the time.note
- A similar oddity hits Rotom-Fan. In its first appearance, it was a Ghost-Electric type with the Levitate ability, which was shared among all Rotom forms then. In the fifth generation, Rotom forms were instead given an appropriate type—which meant that Rotom-Fan became Flying-type. However, it still kept the Levitate ability, which serves to give it certain properties of a Flying-type, even though it's already a Flying-type and has those properties, meaning its ability is redundant to the point of uselessness.note
- Unown has bad stats all around, with its only halfway passable stats being in Attack and Special Attack. But it only knows one move, Hidden Power, which is a Special move, meaning that its Attack stat serves no purpose at all. It's a relic of the days before the physical/special split, meaning that Hidden Power being a physical or special move varying depending on its typing. If an Unown had, say, Hidden Power Rock or Ground, that Attack stat would have actually meant something. After the split occurred in Gen IV though, this was lost, so Unown now has a stat that it can never use for anything.
- In early games, creature names were limited to ten letters, leading to a couple of kludges. The most notable of them was Feraligatr, whose name should really be spelled "Feraligator". The letter limit was raised in Gen VI, but Feraligatr's name forever remains short an "O".