Both are Bug types with a 3 stage evolution - they reach the second stage at level 7 and the final stage at level 10. Both carry the same base stat total through each stage of their evolutionary lines. The Caterpie line is more common in Blue while the Weedle line is more common in Red. This is only true for Metapod and Kakuna in the remakes. Although they are not version-exclusive, both require a Generation III game (FireRed for Caterpie, LeafGreen for Weedle) to be inserted into the DS in order to be encountered in Sinnoh.
In Gold, Silver and their remakes, one can only catch both during the Bug-Catching Contest, otherwise only one can be caught depending on version (Caterpie in Gold and HeartGold, Weedle in Silver and SoulSilver). In Black and White they are fully version-exclusive.
Both are in the Field egg group and evolve at level 22. Ekans is exclusive to Red and FireRed and SoulSilver while Sandshrew is exclusive to Blue and LeafGreen. Both require a Generation III game (FireRed for Ekans, LeafGreen for Sandshrew) to be inserted into the DS in order to be encountered in Sinnoh.
While they are almost the same (both Poison types in the Monster egg group evolving at level 16 and can evolve again using a Moon Stone), they are classified as two separate Pokémon and their evolutions are counterparts being male or female only. Nidoran♂ is more common in Red and FireRed, and Nidoran♀ is more common in Blue and LeafGreen.
Clefairy and Jigglypuff
Both are Fire types that evolve using the Fire Stone. Growlithe is exclusive to Red, Gold, FireRed and HeartGold, while Vulpix is exclusive to Blue, Silver, LeafGreen and SoulSilver. Both require a Generation III game (FireRed for Growlithe, LeafGreen for Vulpix) to be inserted into the DS in order to be encountered in Sinnoh.
Oddish and Bellsprout
They have a 2 stage evolution line and evolve at Level 28. Both are also in the Field egg group. Meowth is exclusive to Blue, Silver and SoulSilver and Mankey is exclusive to Red, Gold and HeartGold.
Both are pure Water types in the Water 3 egg group and evolve using the Water Stone. Both their evolutions are dual-typed (Cloyster gains the Ice-type and Starmie gains the Psychic-type). Cloyster is meant to be a slow defensive Pokémon and Starmie is meant to be a fast attacking Pokémon. Shellder is exclusive to FireRed and Y while Staryu is exclusive to LeafGreen and X.
Hitmonlee and Hitmonchan
Until it was revealed that they had a common pre-evolved form and another alternative evolution, they were considered counterparts. In Generation I, one cannot obtain both without trading.
They are next to each other in the Johto Pokedex and gained an evolution in Generation IV (by level-up while knowing a specific move). Both can learn Power Whip.
Both are Bug types with a base stat total of 500 (as of Generation II). Scyther is exclusive to Red, FireRed and Diamond while Pinsir is exclusive to Blue, LeafGreen and Pearl. In Generation II and their remakes, one can only encounter them through the Bug-Catching Contest.
Electabuzz and Magmar
Both in the Human-Like egg group. Both received pre-evolutions in Generation II and evolutions in Generation IV (by trade while holding a specific item). Electabuzz is exclusive to Red, FireRed and White 2 while Magmar is exclusive to Blue, LeafGreen and Black 2.
They are the first fossil Pokémon introduced. Both are Rock-Water types in the Water 3 egg group that evolve at level 40. In Generation I, FireRed and LeafGreen, one cannot obtain both without trading. Omanyte is exclusive to HeartGold and Alpha Sapphire while Kabuto is exclusive to SoulSilver and Omega Ruby. Both are exclusive to Pokémon X as well.
Both also have Swift Swim and a critical hit-blocking ability (Shell Armor for Omanyte, Battle Armor for Kabuto) as their abilities. Both carry the same base stat total through each stage of their evolutionary lines.
Murkrow and Misdreavus
Both received evolutions in Generation IV (by use of a Dusk Stone). Murkrow is exclusive to FireRed, Diamond and Black while Misdreavus is exclusive to LeafGreen, Pearl and White.
Both are Bug types that evolve once by level-up. Both are version exclusive (with Ledyba in Silver and SoulSilver and Spinarak in Gold and HeartGold). Spinarak can only be encountered at night while Ledyba can only be encountered in the morning. In Sinnoh, only their evolved forms can be encountered.
Both are based on bovine creatures and can only be one gender. Both also have a base stat total of 490. They are one of the less commonly acknowledged counterparts but often appear next to each other in some regional Pokédexes.
Both evolve from Eevee during different times of day (Espeon during the day, Umbreon during the night). Both require high friendship in order to evolve from Eevee. Espeon learns Morning Sun while Umbreon learns Moonlight, both healing moves with different effectiveness during different times of day (in Generation II only).
Both gained evolutions in Generation IV, evolving by leveling up at night while holding a specific item. Both carry the same base stat total through each stage of their evolutionary lines. Both have been version-exclusive - but in different generations, with Delibird acting as the counterpart exclusive to the other version.
Both are Bug types with a base stat total of 500, and both gained Mega Evolutions in Generation VI. In Hoenn, both are found in different areas of the Safari Zone that require different types of bike to access. Pinsir is exclusive to Pokémon X while Heracross is exclusive to Pokémon Y.
Teddiursa is exclusive to SoulSilver while Phanpy is exclusive to HeartGold. They are also version exclusive in Gold and Silver but whichever game they are exclusive to depends on the localization of the game (e.g. Teddiursa is exclusive to Japanese and Korean localizations of Silver while Phanpy is exclusive to all other localizations of Silver).
Both are in the Field egg group and have Pickup as their ability. Their evolutions have different abilities.
Both are Generation VII). Mantine is exclusive to Gold, LeafGreen and HeartGold while Skarmory is exclusive to Silver, FireRed and SoulSilver. Skarmory is tailored towards Defense while Mantine is tailored towards Special Defense.types with a base stat total of 465 (until
Both evolve from Slowpoke. Slowbro evolves by leveling up and Slowking evolves by trading while holding an item.
These legendary version mascots are counterparts and both are leaders of Legendary Trios (Lugia is the master of Articuno, Zapdos, Moltres and Ho-Oh is the master of Raikou, Entei and Suicune). However, neither are exclusive to the versions they are mascots of (although they can be encountered at a lower level in those versions).
Both are Dark types based on canine animals. Poochyena is exclusive to Diamond and White while Houndour is exclusive to Pearl and Black. Both are exclusive to Pokémon X as well.
Both are early-encounter Pokémon that attack Professor Birch (Poochyena in Ruby & Sapphire and Zigzagoon in Emerald). Both also evolve once.
Both are Grass-types, version exclusives and evolve under the same conditions (to get to the second stage, they need to level up to level 14 and to their final stage, they need to have a type of stone used on them). Both require the Generation III game they're exclusive to, to be inserted into the DS in order to be encountered in Sinnoh.
Both carry the same base stat total through each stage of their evolutionary lines. Both have an ability that doubles their speed during a weather condition.
Sableye is exclusive to Sapphire, SoulSilver and Alpha Sapphire while Mawile is exclusive to Ruby, HeartGold and Omega Ruby. Both require the Generation III game they're exclusive to, to be inserted into the DS in order to be encountered in Sinnoh. Both have a base stat total of 380. Both are dual-typed (as of Generation VI) and both also received Mega Evolutions in Generation VI (although Mawile's was released before Sableye's).
They both evolve from Nincada and represent life & death. Shedinja represents death because it is genderless, it belongs to a different egg group than Nincada and Ninjask, and its HP stat never changes.
Despite having no relation in terms of evolution, they look almost identical and their abilities only work when used together. Minun are more common in Ruby and Plusle are more common in Sapphire. In Omega Ruby, Plusle can only be encountered through hordes while this is the case for Minun in Alpha Sapphire. In Black and White they are fully version-exclusive.
Both are Bug-type Firefly Pokémon, have a base stat total of 400 and can only be one gender. Unlike with Tauros and Miltank, one can hatch Volbeat or Illumise from any egg that Illumise breeds with a compatible Pokémon.
Both are dual-type Pokémon that evolve once and are used by villainous teams in the generation they were introduced in (Team Magma uses Camerupt because of its Fire-type and Team Aqua uses Sharpedo because of its Water-type).
The first known rivalry between two different species of Pokémon. Hence, both are version exclusive in Generation III, and both require the Generation III game they're exclusive to, to be inserted into the DS in order to be encountered in Sinnoh. However, both have a base stat total of 458, and both belong to the Field egg group and the Wild Plains friend area in Pokémon Mystery Dungeon: Red Rescue Team and Blue Rescue Team.
They are both genderless, both are Rock/Psychic-types, both version exclusive and represent the sun and moon, which are opposites. Both have a base stat total of 440. Both require the Generation III game they're exclusive to, to be inserted into the DS in order to be encountered in Sinnoh.
They are fossil Pokemon based on marine organisms. Thus, both are partly Rock type and belong to the Water 3 egg group. Both evolve at level 40, and both carry the same base stat total through each stage of their evolutionary lines. While not version-exclusive in those games, one cannot obtain both in Ruby and Sapphire without trading. Both are exclusive to Pokémon Y.
Both are weak Water-type Pokémon based on common fish. They have the same BST and share the same HP & Speed stats. Their Attack, Special Attack, Defense and Special Defense stats are also switched. Magikarp is considered common and Feebas is considered rare. Both can evolve once into dragon-like Water-type Pokémon that share the same BST, HP and Speed stats. They also have switched Attack, Special Attack, Defense and Special Defense. Both of them evolve once (Gyarados for Magikarp and Milotic for Feebas). Gyarados and Milotic also share the same BST and share the same stats swithces and similarities as their pre-evolved forms.
Both are Ghost types that evolve at level 37. Both have a base stat total of 295, with their evolutions' stats totalling up to 455. Duskull gained a further evolution in Generation IV, while Shuppet's evolved form received a Mega Evolution in Generation VI. Duskull is more common in Ruby and Omega Ruby while Shuppet is more common in Sapphire and Alpha Sapphire.
Both evolve from Clamperl by trade with a specific item, are both pure Water-types, and have a base stat total of 485. Huntail is exclusively a wild Pokémon in Black, Black 2 and X while Gorebyss is exclusively a wild Pokémon in White, White 2 and Y, however Clamperl can be found and evolved in both versions.
Both are part of a three-stage evolution that, when fully evolved, are Pseudo-Legendary Pokémon. Both are also introduced in the same generation.
Both are Dragon/Psychic-type Pokémon, gender-exclusive and version-exclusive. In Generations III and IV, one must roam in order to capture whichever is exclusive to their game. An event allows the other (that would otherwise be unavailable) to be encountered and caught.
Version exclusive version mascots which represent the land and the sea. Another example of a red and blue Counter-part.
Although both evolve from Kirlia, they are both very gender oriented, Gardevoir being feminine and Gallade being masculine.
Both are Fossil Pokémon (thus Rock type) that are version exclusive. Both are in the Monster egg group and evolve at level 30.
Both version exclusive (Stunky in Diamond and Glameow in Pearl) and both are used by Team Galactic's Jupiter and Mars respectively. They are also both a two stage evolution and part of the Field egg group. Both Pokémon and their evolution are unavailable in Platinum.
Both are pre-evolutions of earlier generation Pokémon. Both evolve by level-up after learning Mimic (and they can also learn Copycat. Neither are strictly version-exclusive; while Mime Jr. is normally found in Diamond and Bonsly in Pearl, one can obtain Mime Jr. in Pearl or Bonsly in Diamond through the Trophy Garden event unlocked after obtaining the National Pokédex.
Although both evolve from Snorunt, they are very gender oriented, with Glalie being masculine and Froslass being feminine.
Both are Eeveelutions that evolve when leveled up near a special rock.
Version mascots for Diamond and Pearl control Time and Space which are often used together.
Both are related to the moon, Darkrai representing the new moon and Cresselia representing the full moon. Darkrai causes bad dreams and Cresselia cures them.
They both represent the sea and they are parent and child that cannot evolve.
Both are Fighting-type and look similar as if wearing a judo uniform with a black belt. Both have a base stat total of 465. While not version-exclusive in Generation V, in Black and Black 2 Throh can only be encountered in rustling grass. This is true for Sawk in White and White 2. Both became version-exclusive in Generation VI.
Both are Psychic-types in a 3 stage evolution; the second stage is reached at level 32, and the final stage at level 41. Version exclusives.
These fossil Pokemon are based on early turtles and birds. They became version-exclusive starting from Omega Ruby and Alpha Sapphire.
Karrablast and Shelmet
Two Bug-type Pokémon that can only evolve when traded with each other. They also share the same HP and Special Attack stats.
A male and female counterpart pair who are based on American settlers and native Americans. Bothtypes that evolve at level 54. Version exclusives.
These are rivals like Seviper and Zangoose but are NOT version exclusive. However, they both have a base stat total of 484, a base experience yield of 169 and a catch rate of 90.
The ultimate counterparts represent Yin and Yang. Version exclusives.
A Fairy duo based on perfume and sweets. Version Exclusives. Both evolve by trade whilst holding a specific item.
Both are Water-type Pokémon that have the same catch rate and evolve once. Both also have the same HP stat. Version Exclusives.
These fossil Pokemon represent aggression and passion. Both evolve at level 39 but at different times of day. They are also based on different groups of dinosaur (Tyrunt from theropods, Amaura from sauropods).
These counterparts represent X and Y. Version Exclusives.
Both are early-game Normal-type Pokémon that appear during different times of day (Alolan Rattata by night, Yungoos by day). Both have the same BST and capture rate and evolve at Level 20. Their evolved forms are also showcased as Totem Pokémon in both games (Alolan Raticate in Sun & Ultra Sun and Gumshoos in Moon & Ultra Moon).
Both are unevolving Pokémon based on primates. Both of them have the same BST. Both also cancel each others types out (Oranguru's Normal-type is weak to Passimian's Fighting-type while Passimian's Fighting-type is weak to Oranguru's Psychic-type). Version Exclusives.
Both start off as weak Water-type Pokémon that evolve once. Both are dual Water-type Pokémon that are some of the strongest non-legendary Pokémon of their generation. Both are also used by leaders of a villainous team (Lysandre uses Gyarados and Guzma uses Golisopod).
Turtonator and Drampa
Both are unevolving dual-type Dragon-type Pokémon with the same BST. Version Exclusives.
Both are Bug/Fighting-type Ultra Beasts that are Version Exclusives. Both are based on the fight/flight response (Buzzwole is bulky at fighting, a trait used with fight, and Pheromosa is quick at running, a trait used with flight).
Celesteela and Kartana
Both are dual Steel-type Ultra Beasts that are Version Exclusives. Both have the same BST as well. Celesteela is one of the heaviest Pokémon and is made to have high defense while Kartana is one of the lightest Pokémon and is made to have high attack.
Stakataka and Blacephalon
Both are dual-type Ultra Beasts that are Version Exlcusives. Both have the same BST as well. Stakataka is supposed to represent heavy things and weight while Blacephalon is supposed to represent light things and weightlessness.