Name the Odd One Out!

[Jon Watercooler]

Kirlia is the only one who didn't have a split evo path in it's home gen

Enamorus (Therian)
Kyurem (White)
Terapagos
Calyrex

 

[Red Knight]

Terapagos is the only one here who transforms mid-battle and the only one who transforms without the aid of an item (you could say that it uses the Tera Orb to transform, but that's only for its transformation from its Terastal Form to its Stellar Form; its transformation from Normal Form to Terastal Form unambiguously does not use an item).

Only Lunala has a evolutionary line

That is true. I had in mind Palkia, since it is the only one not to have a signature Ability.

Emerald
Platinum
HeartGold/SoulSilver
Black 2/White 2
Omega Ruby/Alpha Sapphire

 

[Jon Watercooler]

ORAS is the only one without some kind of Battle Facility

I had in mind Palkia, since it is the only one not to have a signature Ability.

funny you mentioned that, the intended answer was enamorus since it didn't have a signature ability...

Gogoat
Tapu Koko
Indeedee
Barbaracle
Regigigas

 

[SlipperytheTotodile]

Indeedee changes it's form depending on its gender

(Which Pokemon evolves into a duel type?)

Wiglet
Applin
Gimmighoul
Abra

 

[Dr. Gro 3001]

Both Applin and Gimmighoul. However, Gimmighoul gains an additional type.

Prinplup
Dartrix
Ivysaur
Monferno

 

[SlipperytheTotodile]

Both Applin and Gimmighoul. However, Gimmighoul gains an additional type.

Prinplup
Dartrix
Ivysaur
Monferno

It's just Gimmighoul for the odd one.

Prinplup is the the only none duel type stage 1 starter Pokemon
(Which legendary is a fire type)

Chi-Yu
Tapu Koko
Chein-Pao
Mewtwo

 

[Phantom345]

Chi-Yu.

Metagross
Salamence
Tyrannitar
Dragonite

 

[Dr. Gro 3001]

Metagross is the only one that has no quad weaknesses or is dragonic or dinosaur-like.

Pikachu
Pawmo
Minun
Emolga
Pachirisu

 

[SlipperytheTotodile]

Metagross is the only one that has no quad weaknesses or is dragonic or dinosaur-like.

Pikachu
Pawmo
Minun
Emolga
Pachirisu

Pikachu is the og Pikachu

(Which Pokemon from Kanto evolves in Johto)

Pidgey
Porygon
Pikachu
Electabuzz

 

[guzmania]

that would be my boy porygon

ponyta
vulpix
sandslash
grimer

 

[GelpyK]

Grimer is the only one that shares a type with its original form.

Sticky Hold
Unburden
Flame Body
Infiltrator
Cute Charm

 

[Red Knight]

Cute Charm is the only one not to be possessed by any Pokémon introduced in Scarlet and Violet or its DLC.

ORAS is the only one without some kind of Battle Facility

As pathetically bare-bones as the Battle Maison is, it is still a battle facility.

Emerald
Platinum
HeartGold/SoulSilver
Black 2/White 2
Omega Ruby/Alpha Sapphire

 

[SlipperytheTotodile]

Black 2 and White 2 are Gen 5 games

(Which Pokemon was not introduced in Gen 2)

Totodile
Stanler
Misdreavous
Kingambit

 

[guzmania]

kingambit; to go for other options, one could also say kingambit as it is the only dual-type of the four or totodile as it is the only one that is not part of an evolutionary line that receives a new member in a generation past its introduction.

umbreon
leafeon
vaporeon
espeon

(hint: the intended answer is not vaporeon being introduced in gen 1 or leafeon being introduced in gen 4)

 

[toastghost]

vaporeon has something around its neck, in this case frills

gorebyss
pangoro
drampa
bewear
cacturne

 

[Red Knight]

Gorebyss is the only monotype, the only split evolution, and the only one to evolve with the assistance of an item.

Black 2 and White 2 are Gen 5 games

Sure, but it's not like B2W2 are the only games here not to be from a particular generation. The only two options here that share a generation at all are Platinum and HGSS, so by that logic Emerald and ΩRαS are also the odd ones out.

Emerald
Platinum
HeartGold/SoulSilver
Black 2/White 2
Omega Ruby/Alpha Sapphire

 

[guzmania]

HGSS is the only one to have two visitable regions. emerald is the only one not made for a member of the ds family (including the 3ds). platinum is the only one in which the champion did not receive a redesign (even a minor one, such as wallace's) between their previous and current appearance.

skeledirge
meowscarada
quaquaval

 

[toastghost]

skeledirge is quadraped

Gorebyss is the only monotype, the only split evolution, and the only one to evolve with the assistance of an item.

i was going for pangoro, it doesn't have a particularly dark pokedex entry

mega sableye
mega garchomp
mega sharpedo
mega pinsir
mega tyranitar

 

[Red Knight]

Mega Pinsir is the only one here who does not have a Pokédex entry stating that it suffers some kind of injury or pain from Mega Evolution.

HGSS is the only one to have two visitable regions. emerald is the only one not made for a member of the ds family (including the 3ds). platinum is the only one in which the champion did not receive a redesign (even a minor one, such as wallace's) between their previous and current appearance.

All very good answers that I didn't even think of. Emerald was the answer I was looking for, because it was the only one not to expand its region's Pokédex. (The Platinum and B2W2 expansions are considerably more drastic than the remake expansions, but those do add several Gen 4 evolutions, such as Yanmega, Lickilicky, and Mamoswine in HGSS and Gallade, Probopass, and Magnezone in ΩRαS.)

Steelworker
Steely Spirit
Transistor
Dragon's Maw
Rocky Payload

 

[GelpyK]

Steely Spirit can also boost allies.

Aerilate
Refrigerate
Normalize
Pixilate