Unobtainable Pokémon in later games

Some Pokémon that were originally available in their debut games have become unobtainable in later installments of the Pokémon games.
==In the core series games==
===Pokémon species===
In all core series games up to Pokémon Ultra Sun and Ultra Moon, it was possible to obtain all the previously released Pokémon species by using the available trades or transfers, except in Generation III until certain games were released.
====Generation III====
In , due to the lack of connectivity with previous games, no Pokémon outside the Hoenn Pokédex was legitimately available until the release of later games in this generation. The slogan "Gotta catch 'em all!" was discontinued with the release of Pokémon Ruby and Sapphire.
The Hoenn Pokédex was the first regional Pokédex which did not include all the then-released Pokémon. Although the term "National Pokédex" was introduced in Pokémon Ruby and Sapphire (after it was known as the "Old Pokédex" in the previous generation), it was originally not possible to obtain the National Pokédex in this pair of games due to the lack of trades or transfers from other games.
In Pokémon FireRed, LeafGreen, and Emerald, there are no Pokémon or trades allowed outside their respective regional Pokédexes (either the Kanto Pokédex or the Hoenn Pokédex) until the player obtains the National Pokédex, which is available after entering the Hall of Fame. In FireRed and LeafGreen, there are several Kanto Pokémon that would evolve outside the regional Pokédex (such as into ), but those evolutions are automatically prevented, and Pokémon Eggs cannot be obtained before the National Pokédex either.
The Generation III National Pokédex was eventually able to be completed by obtaining Pokémon from Pokémon Ruby, Sapphire, Colosseum, FireRed, and LeafGreen. Alternatively, once was released, the National Pokédex could be completed using only core series games, with no need to use Pokémon Colosseum.
====Generation VII====
=====Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!=====
 were the first core series games to fully exclude Pokémon species released in previous games, with no means to obtain the excluded Pokémon from any trades, transfers, or events. 
After the introduction of the National Pokédex in Generation III, Pokémon: Let's Go, Pikachu! and Let's Go, Eevee! were the first games to lack the National Pokédex entirely and remain strictly compatible only with the Pokémon in its own regional Pokédex, specifically the Kanto Pokédex. These games are also compatible with the Alolan forms and the Mega Evolutions of these Pokémon.
====Generation VIII====
=====Pokémon Sword and Shield=====
:See also: Pokémon controversy → Pokémon Sword and Shield Pokédex
Pokémon Sword and Shield were the first original games to fully exclude Pokémon species released in previous games. These games are compatible with Pokémon in the Galar Pokédex, Isle of Armor Pokédex, and Crown Tundra Pokédex.
=====Pokémon Brilliant Diamond and Shining Pearl=====
Pokémon Brilliant Diamond and Shining Pearl are compatible with all Pokémon released in the first four generations, as was the case in the Generation IV games.
=====Pokémon Legends: Arceus=====
Pokémon Legends: Arceus is compatible with Pokémon in the Hisui Pokédex.
====Generation IX====
=====Pokémon Scarlet and Violet=====
Pokémon Scarlet and Violet are compatible with Pokémon in the Paldea Pokédex, Kitakami Pokédex, and Blueberry Pokédex.
===Pokémon forms and variants===
Some Pokémon forms and variants are exclusive to certain core series games.
====Generation IV====
=====Pokémon HeartGold and SoulSilver=====
In , the single available Spiky-eared Pichu cannot be traded transferred to any other games.
====Generation VI====
Several Mega Evolutions were introduced in Pokémon X and Y. Some additional Mega Evolutions and the Primal Reversions were introduced in Pokémon Omega Ruby and Alpha Sapphire. They are also available the Generation VII games, but they are unavailable in later generations.
=====Pokémon Omega Ruby and Alpha Sapphire=====
In Pokémon Omega Ruby and Alpha Sapphire, the single available Cosplay Pikachu cannot be traded transferred to any other games.
====Generation VII====
=====Pokémon Sun, Moon, Ultra Sun, and Ultra Moon=====
In Pokémon Sun, Moon, Ultra Sun, and Ultra Moon, the player battles against several Totem Pokémon.
In Pokémon Ultra Sun and Ultra Moon, the are obtainable, but they are not available in later games. The Totem-sized Pokémon based on Pokémon Sun and Moon's Totem Pokémon can be transferred to those games or to Pokémon Bank; however, if transferred to Pokémon HOME, they become normal-sized Pokémon.
Ash-Greninja is obtained in Pokémon Sun and Moon and remains available Pokémon Ultra Sun and Ultra Moon. However, it is unobtainable from Generation VIII onwards.
Ultra Necrozma is exclusive to Pokémon Ultra Sun and Ultra Moon due to the need to hold the Ultranecrozium Z.
=====Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!=====
In , the single available Partner Pikachu or Eevee cannot be traded or transferred to any other games.
====Generation VIII====
=====Pokémon Sword and Shield=====
All the Gigantamax forms are exclusive to Pokémon Sword and Shield.
==In the side series games==
===Pokémon Stadium series===
In the Japanese Pokémon Stadium, only 40 of the 151 Pokémon in existence at the time could be brought to battle from the core series games by using the Transfer Pak. The second game in the series, and the first one to be released worldwide, would later add compatibility with all the remaining Pokémon.
===Pokémon HOME===
In Pokémon HOME, the compatibility with each core series game was usually introduced months after the release of each game.
==In the spin-off games==
===Pokémon Mystery Dungeon series===
In the Pokémon Mystery Dungeon series, several games include all the then-released Pokémon. However, there are some exceptions.
====Pokémon Mystery Dungeon: Gates to Infinity====
In Pokémon Mystery Dungeon: Gates to Infinity, which was released during Generation V, there are 144 recruitable species of Pokémon. A further 6 species appear as NPCs or bosses, and are not recruitable.
====Pokémon Mystery Dungeon: Rescue Team DX====
In Pokémon Mystery Dungeon: Rescue Team DX, a Generation VII remake of Red Rescue Team and Blue Rescue Team, the 386 Pokémon released up to Generation III are obtainable, as well as any pre-Evolutions, evolutions, and Mega Evolutions added for those species in generations IV-VII. and are included as well. However, Alolan Forms are not included.
===Pokémon Snap series===
In the Pokémon Snap series, both games have a limited pool of available Pokémon: Pokémon Snap has 63 species and New Pokémon Snap has 234 species. However, several Pokémon from the first game are missing in the second game nonetheless.
===Pokémon Pinball series===
In the original Pokémon Pinball, all the then-released Pokémon in Generation I were available. However, in Pokémon Pinball: Ruby & Sapphire, only the Pokémon in the Generation III Hoenn Pokédex, except , with the addition of , , , and were obtainable.
===Super Smash Bros. series===
In the Super Smash Bros. series, each game has included new Pokémon available as fighters. However, some Pokémon have been removed as well.
====Super Smash Bros. Brawl====
In Super Smash Bros. Brawl, and are absent as fighters. Mewtwo returned in Super Smash Bros. for Nintendo 3DS/Wii U. Pichu returned in Super Smash Bros. Ultimate.
====Super Smash Bros. for Nintendo 3DS/Wii U====
In Super Smash Bros. for Nintendo 3DS/Wii U, in addition to , the and his and are absent as well. Instead, the player controls only directly, which was previously one of the Pokémon Trainer's Pokémon. The Pokémon Trainer returned in Super Smash Bros. Ultimate.
==See also==
* Pokémon availability
Category:Game mechanics