Odd One Out

[Ghost Lunis]

emolga is the only non steel type

hmm...vivillon, unown, and pikachu

 

[Virtual Headache]

Unown, because it is not animal like, genderless and also can't breed unlike the other two.

Diancie, Mewtwo and Charizard.

 

[Apollo]

Diancie wasn't a childhood favorite. :P
Charizard was the only one owned by Ash.

Wurmple, Butterfree, Swadloon

 

[Nah]

Swadloon is the only one that requires high levels of happiness in order to evolve.

Cradily, Aerodactly, Terrakion

 

[Renegade]

Aerodactly isn't a Pokemon. xD
I'm very sorry for that one, by the way...

Shroomish, Tepig, & Celebi~

 

[Apollo]

Tepig isn't weak to bug-types!

Oshawott, Azumarill, Charmander

 

[Judge Mandolore Shepard]

Charmander is not a Water type

How about Azurill, Samurott, Blastoise

 

[classiccartoonsftw]

Azurill isn't a Water type, a starter, or fully evolved.

Meowstic, Jellicent, and Hippowdon

 

[Nah]

Meowstic is the only one who's abilities and movepools, and not just appearances, vary depending on its gender.

Cradily, Gastrodon, Poliwrath

 

[Apollo]

Poliwrath wasn't owned by a champion.

Dragonite, Metagross, Tyranitar

 

[Renegade]

The Metagross branch is not available in the wild.

Ponyta, Krookodile, & Piloswine~

 

[Apollo]

Ponyta isn't weak to fighting.

Froslass, Durant, Piplup

 

[Warship]

Durant is the only one that cant learn Ice Beam(or any ice attacks for that matter).

Vibrava, Gloom, Tangrowth

 

[Lusus]

Tangrowth is the only one that doesn't have 2 types

Porygon, Kadabra, Haunter

 

[Ghost Lunis]

porygon is the only one that needs to hold an item in order to evolve when trading.

modern vivillon, high plains vivillon, monsoon vivillon

 

[Rosehip]

Monsoon Vivillon uses cool colours while the others use warmer ones. Also, Monsoon Vivi isn't found in the US unlike the others, according to the Vivillon map.

Unfezant, Staraptor, Pidgeot.

 

[Tsutarja]

Unfezant can have different appearances based on which gender it is.

Infernape, Emboar, Delphox

 

[Hikamaru]

Delphox is the only one that isn't Fire/Fighting.

Pumpkaboo, Sandile, Wingull

 

[Tsutarja]

This may be a bit different than you'd expect, but Pumpkaboo is the only one that didn't make its debut in an odd-numbered generation.

Hippopotas, Pikachu, Helioptile

 

[Rosehip]

Pikachu is the only one that isn't in the Little Cup competitive tier.

Moltres, Xerneas, Eelektross.