Odd One Out

[Sonata]

Darmanitan is the only one that can change its form during battle

Meowth, Snorlax, Tauros

 

[Kameken]

Darmanitan isn't a fighting type, first off

Tauros is the only quadrupedal one.

Mawile, probopass, magnemite

 

[Juno]

Mawile is the only one with a Mega Evolution.

Treecko, Turtwig, and Snivy?

 

[orangeralts21]

Turtwig is the only one who gains a secondary type as it evolves.

Fearow, Smoochum and Toxicroak

 

[Juno]

Smoochum is the only female-only Pokemon.

Bouffalant, Tauros and Stantler?

 

[Judge Mandolore Shepard]

Stantler was the only one that was introduced in a even numbered gen

Skarmory, Altaria, Pidgeot

 

[Nah]

Skarmory is the only one without any pre-evolutions.


Diglett, Shuppet, Chikorita

 

[orangeralts21]

Chickorita is the only one with a line that evolves twice.

Omastar, Castcoon and Clefable

 

[KKJ]

Cascoon is the only non fully evolved one
Raikou, Regice or Tornadus

 

[Juno]

Tornadus is the only one with a gender - Raikou and Regice are genderless.

Mienfoo, Mankey and Makuhita?

 

[Judge Mandolore Shepard]

Makuhita is the only one used by a Gym Leader

Gengar, Miltank, and Vivillon

 

[Kameken]

Korrina uses a mienfoo in her gym, actually.

Miltank has only one type.

Pidgey, pidove, fletchling.

 

[Sonata]

Fletchling is the only one not used by a gym leader.

Bisharp, Tyranitar, Scizor

 

[DraconianWing]

Tyranitar is the only one who isn't a Steel type.

Aggron, Nidoking, Gardevoir

 

[Wicked3DS]

Nidoking is the only one without a Mega Evolution.

Golduck, Seaking, Kingler

 

[orangeralts21]

Seaking is the only one based on a fully aquatic animal.

Geodude, Onix, Rhyhorn

 

[Nah]

Onix is the only one that has a type change when it evolves.

Buziel, Gastrodon, Marshtomp

 

[Juno]

Buizel is the only pure Water-type.

Oddish, Bellsprout and Budew?

 

[Hikamaru]

Budew, it's the only one whose final evolution stage doesn't evolve with use of a Leaf Stone.

Spritzee, Electrike, Clauncher

 

[Wicked3DS]

Electrike is the only one not introduced in Gen VI.

Muk, Arbok, Weezing