Novelty Pokémon

A novelty Pokémon, also referred to as a gimmick Pokémon, is a term for a Pokémon that usually possesses at least one of the following characteristics:

Has a movepool limited to very few moves
Has a unique Ability
Is considered by some to have been made to introduce a game mechanic
Has another unique feature

These Pokémon are often hard to come by, and may be simply given to the player once per game.

Some of these Pokémon are difficult to use in competitive battling, but became viable participants in Pokémon Contests after they were introduced in Generation III. Generation IV introduced the Pokéathlon which allows any Pokémon to compete by giving each Pokémon its own special set of stats.

List of novelty Pokémon

Pokémon		Reason
063	Abra	Abra was a novelty Pokémon in the first generation as it and its evolutions were the only Pokémon capable of learning Teleport by level-up. It is also the only move Abra can learn by level-up, which makes capturing wild Abra incredibly difficult.
083	Farfetch'd	Farfetch'd was a novelty Pokémon in the first generation due to the fact that it could only be acquired by an in-game trade, though it could be caught in the wild in Pokémon Yellow. In Generation II, Farfetch'd was also given its own unique novelty item, the Stick.
108	Lickitung	Lickitung was a novelty Pokémon in the first generation due to the fact that it could only be acquired by an in-game trade, though it could be caught in the wild in Pokémon Yellow.
122	Mr. Mime	Mr. Mime was a novelty Pokémon in the first generation due to the fact that it could only be acquired by an in-game trade, and was unobtainable any other way, other than by trading from Generation II.
124	Jynx	Jynx was a novelty Pokémon in the first generation due to the fact that it could only be acquired by an in-game trade, and was unobtainable any other way, other than trading from Generation II. Jynx is also the only Pokémon to undergo a major redesign, due to the alleged controversy surrounding it in the US. It remains the only Pokémon which can learn Lovely Kiss by level-up.
132	Ditto	Ditto only has one move—Transform—which lets it copy the appearance, types, moves, and stats (excluding HP) of its target. From Generation II onwards Ditto is able to breed with any Pokémon outside of the Undiscovered Egg Group. In Generation V it became the only Pokémon with access to the new Ability Imposter, which automatically transforms the user into the opponent.
133	Eevee	Eevee was a novelty Pokémon in the first generation as it was used to showcase an evolution method, the evolutionary stones. Eevee was also the only Pokémon to have a branched evolution. After Generation I, Eevee has been relegated to simply having the most evolutions.
151	Mew	Mew has the unique capability to learn every TM, HM and Move Tutor move (except those exclusive to a particular Pokémon or group of Pokémon, such as Draco Meteor and Secret Sword), and as such, Mew has the largest movepool of all Pokémon. Mew was also the first Pokémon to be available exclusively by an event, and the only one in Generation I.
172	Spiky-eared Pichu	While Pichu are not considered to be novelty Pokémon, the Spiky-eared variant found only in HeartGold and SoulSilver can be considered to be a novelty form. Spiky-eared Pichu cannot evolve, cannot be traded to any other game and has the same base stats as normal Pichu. However, it does have different Pokéathlon stats. Spiky-eared Pichu is considered by some to be a marketing tool used to promote the Pokémon movie Arceus and the Jewel of Life, in which a Spiky-eared Pichu appears as one of the main characters. Spiky-eared Pichu is also the second form difference not to be carried over into later games in the main series (the first being Shadow Lugia from Pokémon XD: Gale of Darkness), as it cannot be transferred to Generation V games.
175	Togepi	Togepi was a novelty Pokémon in Generation II due to the fact that only one could be obtained, from Professor Elm's assistant, and was to showcase the addition of Pokémon Eggs and breeding.
183	Marill	Marill, like Plusle, Minun, Pachirisu and Emolga, is considered by some to have been a marketing tool, created to use the popularity of Pikachu (which it has a slight resemblance to) to promote Generation II.
201	Unown	Unown’s main purpose in the games is to be collected, a sidequest that consists of finding its 28 forms. It is capable of learning only one move.
202	Wobbuffet	Wobbuffet has very high HP, but is only capable of learning four moves, and a further three from its pre-evolution Wynaut. Also along with Wynaut it was the only Pokémon with the Shadow Tag Ability prior to Generation V.
213	Shuckle	Shuckle has very high Defense and Special Defense, making it extremely tough. But it has very low HP, Attack and Special Attack, and it is tied with Munchlax for the lowest Speed of any Pokémon. However, it was capable of creating Berry Juice and eventually valuable Rare Candies in Generation II if it held a Berry.
225	Delibird	Delibird is capable of naturally learning only a single move and is the only Pokémon who can learn it naturally. Unlike Unown, it can learn other moves via TMs and breeding.
235	Smeargle	Smeargle learns only one move repeatedly, but this move has the ability to permanently duplicate the moves of other Pokémon. With the capability to learn every move, it is very useful in breeding egg moves to Pokémon.
236	Tyrogue	Tyrogue is a novelty Pokémon due to the fact that it is the only Pokémon to link two previously unrelated Pokémon into an evolution family. It is also the only Pokémon that evolves based on its stats.
292	Shedinja	Shedinja is protected from most attacks due to Wonder Guard, but it is also the only Pokémon to have 1 HP, the lowest base stat of any known Pokémon. In addition, it has a unique evolution method.
302	Sableye	Sableye was the only Pokémon with no weaknesses until Spiritomb was introduced in Generation IV, however, in said generation it became the only Pokémon to have access to the Ability Stall.
311 312	Plusle and Minun	Plusle and Minun are considered by some to have been created to showcase the Double Battle addition to the series in Generation III. Like Marill, Pachirisu, and Emolga, they are also considered by some to be a marketing tool, created to use the popularity of Pikachu (which they resemble) to promote Generation III.
327	Spinda	Spinda’s main gimmick is the variable designs on its body, in a bit of an expansion of the Unown concept.
349	Feebas	Feebas was a novelty Pokémon prior to Generation V due to the fact that Feebas could only evolve into Milotic when its Beauty condition was high. In Generation V, Feebas can now also evolve by trading it while holding the Prism Scale, though it remains the only Pokémon to at some point have been able to evolve based on contest condition.
351	Castform	Castform has a unique Ability to change form and type depending on the weather. It was also the only Pokémon to learn Weather Ball until Generation IV.
352	Kecleon	Kecleon has a unique Ability that causes it to change its type to match whatever attack it is hit by.
370	Luvdisc	Luvdisc can be found holding Heart Scales, which can be given to move relearners in exchange for their services.
386	Deoxys	Deoxys is capable of changing between four different forms. Deoxys was also the first Pokémon whose base stats and move compatibility differed between forms. Deoxys's forms can be changed at will in Generation IV and onwards, however, they were game-specific in Generation III, with Deoxys being the only Pokémon with this distinction.
412 413	Burmy and Wormadam	Burmy, Wormadam, and their various cloaks are considered to be an example of both the location based evolutions and the gender based evolutions.
412	Cherrim	Cherrim has two forms which change during intense sunlight, the Overcast Form and the Sunny Form. Cherrim also has a unique Ability.
417	Pachirisu	Pachirisu, like Marill, Plusle, Minun and Emolga, is considered by some to have been a marketing tool, created to use the popularity of Pikachu (which it resembles) to promote Generation IV.
422 423	Shellos and Gastrodon	Shellos and Gastrodon each have two different forms, West Sea and East Sea, which vary depending on what side of Mt. Coronet they are found.
441	Chatot	Chatot can use Chatter to repeat back messages recorded on the DS microphone.
442	Spiritomb	Spiritomb is considered by some to have been used to showcase the Sinnoh Underground from Generation IV, and is considered a novelty due to the unique way it is captured, by taking the Odd Keystone to the Hallowed Tower, and then talking to people in the Underground 32 times, then returning to the tower to battle a wild Spiritomb. It is also the second Pokémon with no weaknesses, after Sableye.
479	Rotom	Rotom is capable of changing between six different forms. Until Generation V, all forms of Rotom were Electric/Ghost-type. Rotom is one of only three Pokémon to undergo a type change, and the only one to have one of its types removed, though this does not apply to Rotom's normal form.
489 490	Phione and Manaphy	Phione can only be obtained by breeding the event Pokémon Manaphy, with Manaphy being the only legendary Pokémon capable of breeding. Although Manaphy produces Phione eggs when bred with Ditto, Phione cannot evolve into Manaphy.
493	Arceus	Arceus has a unique Ability that enables it to change its Forme and type depending on the Plate it is holding. Arceus also has the highest base stat total of all known Pokémon.
550	Basculin	Basculin is the only Pokémon that has four different abilities. It also has two different forms, with the rarity of each form differing between Pokémon Black and White.
555	Darmanitan	Darmanitan found in the Desert Resort, have a unique Ability which enables it to change between two different forms, its Standard Mode and its Zen Mode. However, Regular Darmanitan do not have this Ability.
585 586	Deerling and Sawsbuck	Deerling and Sawsbuck each have four different forms that vary depending on the current in-game season, and their various forms are considered by some to showcase the addition of seasons to the series.
587	Emolga	Emolga, like Marill, Plusle, Minun and Pachirisu, is considered by some to be a marketing tool, created to use the popularity of Pikachu (which it resembles) to promote Generation V.
648	Meloetta	Meloetta is the only Pokémon that can learn Relic Song, a move which allows Meloetta to switch between its two Formes, its Aria Forme and its Pirouette Forme.
649	Genesect	Genesect can change its appearance and the type of its signature move Techno Blast, depending on the Drive it is holding.