Including its most recent addition, Pokemon has a massive 18 types to classify different Pokemon. Because Pokemon can have two types at once, there are 171 different unique combinations. In spite of the fact that there are 890 Pokemon, 25 of these type combinations are unique to single Pokemon. What's more, 9 of them have not ever been used by a Pokemon, meaning there are still a lot of possibilities for new Pokemon in future generations to claim spots as Pokemon with unique type combinations.
The Pokemon listed here all are unique because no other Pokemon shares their typing. For the sake of clarity, it should be said that the order of typing doesn't matter, meaning a Fire/Dark Pokemon would be considered the same as a Dark/Fire Pokemon. There are also several Pokemon whose entire evolution chain is of a unique type (Zubat, Golbat, and Crobat are the only Poison/Flying type Pokemon, for example), but these will not be included because there is technically more than one Pokemon with that type. Legendary Pokemon, Mega Evolutions, and Gigantamax forms will also be considered, and these rules leave 25 Pokemon with unique type combinations in the Pokemon franchise.
Updated on August 10, 2023, by Ben Painter: With new Pokemon announced in every new generation, the Pokemon that have unique type combinations grow smaller. This list adds every Pokemon or the same ones in an evolution line with a unique type combination that no other Pokemon shares. There are still 9 combinations that do not have a single Pokemon that has that typing, perhaps one-day fans will have every single typing that could be.
Bibarel (Normal/Water)
Bibarel is an odd case as it evolves from the pure Normal type Bidoof and gains the Water type as a result. Because Bidoof doesn't also have this type, Bibarel is the only one of its kind.
This Pokemon and its predecessor are the butt of many Pokemon jokes so no doubt most are already familiar with them. Its typing makes it immune to Ghost and grants resistance to Steel, Fire, Water, and Ice, but he can still be taken down by Fighting, Grass, and Electric moves with ease.
Crabominable (Fighting/Ice)
Crabominable's typing is a great concept, but results in less than favorable strengths and weaknesses.
This Pokemon is weak to six types (Fighting, Flying, Steel, Fire, Psychic, and Fairy) and only resists 3 (Bug, Ice, and Dark). It seems that for the most part, these two types cancel out each others' strengths rather than complement them.
Galarian Slowking/Slowbro (Poison/Psychic)
Slowbro was released in the original 151 and has been a staple of the franchise for many years now, it has been shown a lot of love in the past, even getting a Mega Evolution. But GameFreak was not done there and in Pokemon Sword & Shield's DLCs both Slowbro and Slowpoke's other evolution received new forms in Galar.
Both Galarian Slowbro and Slowking are Poison and Psychic types, this evolution line is the only Pokemon with this typing making them both rare Pokemon. Comparing the Galar forms to the regular forms which are Psychic and Water the newer 'mons have two fewer weaknesses only being 2x affected by Ghost, Dark, and Ground. An improvement to say the least.
Galarian Weezing (Poison/Fairy)
Aside from having an amazing design, Galarian Weezing stands out for having the Fairy type. This typing is relatively new to Pokemon and sort of acts as a foil to the powerful Dragon type.
Including Fairy in Galarian Weezing's typing is a huge boon, as the only weakness it adds is the relatively uncommon Steel type while it boosts his resistances substantially, even making him immune to Dragon.
Terrakion (Rock/Fighting)
One would think that the Rock and Fighting type wouldn't be uncommon, but surprisingly only Terrakion possesses it. There may be a good reason for that, though, as this type is rife with weaknesses.
Terrakion is weak to Fighting, Ground, Steel, Water, Grass, Psychic, and Fairy, but has a decent array of resistances to make up for it, including Normal, Poison, Rock, Bug, Fire, and Dark.
Tyranitar (Rock/Dark)
Tyranitar's Dark typing is iconic but accentuates its greatest weakness, the Fighting type. As a sort of trade-off, it also gives the Pokemon an immunity to Psychic which is helpful, but other than that Tyranitar's weaknesses and resistances are completely spread even, with 6 in each category.
Tyranitar is a fan-favorite Pokemon and it is on many trainers' teams throughout all of the generations, the fact that it is the only Rock and Dark type in the franchise only adds bonus points to the Godzilla of the Pokemon universe.
Shedinja (Bug/Ghost)
The Pokedex calls Shedinja a "discarded bug shell that came to life," and if that isn't creepy enough to justify its Ghost-type then nothing is.
While Bug is generally considered a weak type, the Ghost type complements it well. Although it doesn't negate any weaknesses (actually adding Ghost and Dark instead), it does strengthen what the Bug-type was already good at. What makes Shedinja even more unique is that it has 1 HP, but this is backed up by the fact it cannot be hit by any move that isn't super effective against it, in the right circumstances this Pokemon can be completely invincible.
Heatran (Fire/Steel)
The first Legendary Pokemon is Heatran, who is Fire/Steel. Given that Steel types are weak to Fire, the Pokedex entry comment about it melting its own steel makes a lot of sense.
As a type combo, however, the Fire-type negates that weakness and together provides a pretty durable Pokemon. Ground-type moves should be avoided at all costs, however, as it is 4x weak to this type and one Earthquake would mean the end for Heatran.
Volcanion (Fire/Water)
Perhaps even more oxymoronic than the last, Volcanion is the only Fire/Water type Pokemon. As such, Volcanion is weak to Ground, Rock, and Electric attacks but is either neutral or resistant to everything else. This is also the first Mythical Pokemon listed here.
This Pokemon's whole gimmick is steam, which makes sense because fire and water make steam. Volcanion is such a rare find, it cannot be obtained in regular gameplay, only in events, so this unique type is virtually nonexistent.
Empoleon (Water/Steel)
The Generation 4 starters were very unique in their typings, as Empoleon proves with its Water and Steel type. Both of these types are considered very defensive types, so it is no surprise that the combination is as well.
Empoleon has eight resistances, two double resistances, and even one immunity. It is a crying shame that only Empoleon is this type, but that makes the loved Sinnoh starter even more special.