Litleo was the first Fire/Normal type, it and Pyroar are also the only Fire/Normal types
Bibarel was the first Water/Normal type, it is also the only Water/Normal type
Helioptile was the first Electric/Normal type, it and Heliolisk are also the only Electric/Normal types
Deerling was the first Grass/Normal type
Pirouette Meloetta is the first Fighting/Normal type
Shroodle was the first Poison/Normal type, it and Grafaiai are also the only Poison/Normal types
Diggersby was the first Ground/Normal type
Pidgey was the first Flying/Normal type
Girafarig was the first Psychic/Normal type
Hisuian Zorua was the first Ghost/Normal type, it and Hisuian Zoroark are also the only Ghost/Normal types
Drampa was the first Dragon/Normal type
Alolan Rattata was the first Dark/Normal type
Jigglypuff was the first Fairy/Normal type
Volcanion was the first Water/Fire type, it is also the only Water/Fire type
Heat Rotom was the first Electric/Fire type, it is also the only Electric/Fire type
Scovillain was the first Grass/Fire type, it is also the only Grass/Fire type
Zen Mode Galarian Darmanitan was the first Ice/Fire, it is also the only Ice/Fire type
Combusken was the first Fighting/Fire type
Salandit was the first Poison/Fire type, it and Salazzle are also the only Poison/Fire types
Numel was the first Ground/Fire type
Charizard was the first Flying/Fire type
Victini was the first Psychic/Fire type
Larvesta was the first Bug/Fire type
Magcargo was the first Rock/Fire type
Litwik was the first Ghost/Fire type
Reshiram was the first Dragon/Fire type
Houndour was the first Dark/Fire type
Heatran was the first Steel/Fire type, it is also the only Steel/Fire type
Chinchou was the first Electric/Water type
Lotad was the first Grass/Water type, it Lombre and Ludicolo are also the only Grass/Water types
Dewgong was the first Ice/Water type
Poliwrath was the first Fighting/Water type
Tentacool was the first Poison/Water type
Wooper was the first Ground/Water type
Gyarados was the first Flying/Water type
Slowpoke was the first Psychic/Water type
Surskit was the first Bug/Water type
Omanyte was the first Rock/Water type
Frillish was the first Ghost/Water type
Kingdra was the first Dragon/Water type
Carvanha was the first Dark/Water type
Empoleon was the first Steel/Water type, it is also the only Steel/Water type
Marill was the first Fairy/Water type
Mow Rotom was the first Grass/Electric type
Frost Rotom was the first Ice/Electric type
Pawmo was the first Fighting/Electric type
Toxel was the first Poison/Electric type, it and both of Toxtricity's forms + Gmax are the only Poison/Electric types
Stunfisk was the first Ground/Electric type
Zapdos was the first Flying/Electric type
Alolan Raichu was the first Psychic/Electric type, it is also the only Psychic/Electric type
Joltik was the first Bug/Electric type
Alolan Geodude was the first Electric/Rock type
Rotom was the first Ghost/Electric type, it is also the only Ghost/Electric type
Zekrom was the first Dragon/Electric type
Morpeko was the first Dark/Eelectric type, it is also the only Dark/Electric type
Magnemite was the first Steel/Electric type
Dedenne was the first Fairy/Electric type
Snover was the first Ice/Grass type, it Abomasnow and Mega Abomasnow are also the only Ice/Grass types
Breloom was the first Fighting/Grass type
Bulbasaur was the first Poison/Grass type
Torterra was the first Ground/Grass type
Hoppip was the first Flying/Grass type
Lileep was the first Rock/Grass type, it and Cradily are also the only Rock/Grass types
Mega Sceptile was the first Dragon/Grass type
Nuzleaf was the first Dark/Grass type
Ferroseed was the first Steel/Grass type
Cottonee was the first Fairy/Grass type
Crabominable was the first Fighting/Ice type, it is also the only Fighting/Ice type
Swinub was the first Ground/Ice type, it Piloswine and Mamoswine are also the only Ground/Ice types
Articuno was the first Flying/Ice type
Snom was the first Bug/Ice type, it and Frosmoth are also the only Bug/Ice types
Jynx was the first Psychic/Ice type
Amaura was the first Rock/Ice type
Froslass was the first Ghost/Ice type, it is also the only Ghost/Ice type
Kyurem was the first Dragon/Ice type
Sneasel was the first Dark/Ice type
Alolan Sandshrew was the first Steel/Ice type, it and Alolan Sandslash are also the only Steel/Ice types
Alolan Ninetales was the first Fairy/Ice type, it is also the only Fairy/Ice type
Croagunk was the first Poison/Fighting type
Hawlucha was the first Flying/Fighting type
Meditite was the first Psychic/Fighting type
Heracross was the first Bug/Fighting type
Great Tusk was the first Ground/Fighting type, it is also the only Ground/Fighting type
Terrakion was the first Rock/Fighting type, it is also the only Rock/Fighting type
Marshadow was the first Ghost/Fighting type
Hakamo-o was the first Dragon/Fighting type
Scraggy was the first Dark/Fighting type
Lucario was the first Steel/Fighting type
Iron Valiant was the first Fairy/Fighting type, it is also the only Fairy/Fighting type
Nidoqueen was the first Ground/Poison type
Zubat was the first Flying/Poison type, it Golbat and Crobat are also the only Flying/Poison types
Galarian Slowbro was the first Psychic/Poison type, it and Galarian Slowking are also the only Psychic/Poison types
Weedle was the first Bug/Poison type
Nihilego was the first Rock/Poison type
Gastly was the first Ghost/Poison type, it Haunter, Gengar, and Mega Gengar are also the only Ghost/Poison types
Dragalge was the first Dragon/Poison type
Stunky was the first Dark/Poison type
Varoom was the first Steel/Poison type, it and Revavroom are also the only Steel/Poison types
Galarian Weezing was the first Fairy/Poison type, it is also the only Fairy/Poison type
Gligar was the first Flying/Ground type
Baltoy was the first Psychic/Ground type, it and Claydol are also the only Psychic/Ground types
Nincada was the first Bug/Ground type
Geodude was the first Rock/Ground type
Golett was the first Ghost/Ground type
Vibrava was the first Dragon/Ground type
Sandile was the first Dark/Ground type
Steelix was the first Steel/Ground type
Natu was the first Psychic/Flying type
Butterfree was the first Bug/Flying type
Aerodactyl was the first Rock/Flying type
Drifloon was the first Ghost/Flying type
Dragonite was the first Dragon/Flying type
Murkrow was the first Dark/Flying type
Skarmory was the first Steel/Flying type
Togetic was the first Fairy/Flying type
Dottler was the first Bug/Psychic type
Lunatone was the first Rock/Psychic
Hoopa Confined was the first Ghost/Psychic type
Latias was the first Dragon/Psychic type
Inkay was the first Dark/Psychic type
Beldum was the first Steel/Psychic type
Mr. Mime was the first Fairy/Psychic** type
Shuckle was the first Rock/Bug type
Shedinja was the first Ghost/Bug type, it is also the only Ghost/Bug type
Forretress was the first Steel/Bug type
Cutiefly was the first Fairy/Bug type, it and Ribombee are also the only Fairy/Bug types
Lokix was the first Dark/Bug type, it is also the only Dark/Bug type
Tyrunt was the first Dragon/Rock type, it and Tyrantrum are also the only Dragon/Rock types
Tyranitar was the first Dark/Rock type, it and its mega evolved form are also the only Dark/Rock types
Aron was the first Steel/Rock type
Carbink was the first Fairy/Rock type
Giratina was the first Dragon/Ghost type
Sableye was the first Dark/Ghost type
Honedge was the first Steel/Ghost type
Mimikyu was the first Fairy/Ghost type
Deino was the first Dark/Dragon type
Dialga was the first Steel/Dragon type
Mega Altaria was the first Fairy/Dragon type, it is also the only Fairy/Dragon type
Impidimp was the first Fairy/Dark type, it Morgrem and Grimmsnarl are also the only Fairy/Dark types
Pawniard was the first Steel/Dark type, it Bisharp and Kingambit are also the only Steel/Dark types
Mawile was the first Fairy/Steel type
Edit from Meta Ridley: Some Pokemon received the Fairy type along with their original type in Generation 6, making them the first Pokemon to have their own dual typing
2020 Edit:
-I added the new Pokemon from Galar
-Alolan Rattata and Raticate are no longer the only Dark/Normal types
-Larvesta and Volcarona are no longer the only Bug/Fire types
-Magcargo is no longer the only Rock/Fire type
-Frost Rotom is no longer the only Ice/Electric type
-Jynx and Smoochum are no longer the only Psychic/Ice type
-Hawlucha is no longer the only Fighting/Flying type
-Giratina is no longer the only Dragon/Ghost type
-Dialga is no longer the only Steel/Dragon type
2022 Edit:
-I added the new Pokemon from Hisui and Paldea
-I added Pokemon that previously had accidentally been missing from the list
-Deerling and Sawsbuck are no longer the only Grass/Normal types
-Diggersby is no longer the only Ground/Normal type
-Drampa is no longer the only Dragon/Normal type
-Salandit and Salazzle are no longer the only Poison/Fire types
-Frillish and Jellicent are no longer the only Ghost/Water types
-Mow Rotom is no longer the only Grass/Electric types
-Stunfisk is no longer the only Ground/Electric type
-Alolan Geodude, Graveler, and Golem are no longer the only Rock/Electric types
-Torterra is no longer the only Ground/Grass type
-Amaura and Aurorus are no longer the only Rock/Ice types
-Kyurem and its alternate forms are no longer the only Dragon/Ice types
-Sneasel and Weavile are no longer the only Dark/Ice types
-Nihilego is no longer the only Rock/Poison type
-Croagunk and Toxicroak are no longer the only Poison/Fighting types
-Marshadow is no longer the only Ghost/Fighting type
-Hakamo-o and Komoo-o are no longer the only Dragon/Fighting types
-Sandile, Krokorok, and Krookodile are no longer the only Dark/Ground types
-Togetic and Togekiss are no longer the only Fairy/Flying types
-Dottler and Orbeetle are no longer the only Bug/Psychic types
-Honedge, Doublade, and Aegislash are no longer the only Steel/Ghost types
-Mimikyu is no longer the only Fairy/Ghost type
