Odd One Out

[Lycanthropy]

Sceptile is the only one not learning Synthesis through levelling.

Magcargo, Mamoswine, Magnezone

 

[daniilS]

Mamoswine's name doesn't start with Mag.

Milotic, Mightyena, Misdreavus

 

[Emboar]

Misdreavus is not in the Hoenn Pokedex.

Chinchou, Chingling, Chimchar.

 

[daniilS]

Chimchar, its Japanese name doesn't have a long sound (ー).

Emboar, Giratina, Staravia

 

[antemortem]

Dialga's the only one without a Fire-type weakness, as it's neutral.

Azurill, Marill, Azumarill

 

[Foamster-Whiskey]

Kyurem is the only legendary

Eelektross, Raichu, Magnezone

 

[antemortem]

Magnezone lacks feet of some sort.

Goldeen, Vulpix, Trubbish

 

[Mawa]

Pangoro is the only one who's not from Hoenn.

Jynx, Glaceon, Jigglypuff

 

[daniilS]

Eevee has a higher chance to be male than to be female.

Jolteon, Snivy, Relicanth

 

[faf]

Relicanth is a dual type.

Druddigon, Haxorus, Dragonair

 

[bunny24680]

This is a hard one but still, I think Sceptile is odd one as it is the only one belonging to a starter family and is the only one whose mega evolution's type is different from original....

Find odd one: Spearow, Taillow, Hoothoot

 

[Illuminarty]

Tailow, it's the only one to learn a fighting move (Quick Guard) naturally

Aipom, Mankey, Monferno

 

[Illuminarty]

Starmie, it has no eyes.

Zubat, Bellossom, Luvdisc

 

[bunny24680]

Zubat, for the same reason given above i.e. no eyes while other two have eyes.....

Zubat, Golbat, Crobat

 

[DyingWillFlareon]

Bidoof, as it is the only one without a 4x weakness. :3

Honchcrow, Cinccino, Watchog

 

[Admison]

Honchkrow is the only one that isn't a normal type.

Weedle, Wurmple, Caterpie

 

[DyingWillFlareon]

Caterpie doesn't learn Poison Sting.

Braviary, Doublade, Xerneas.

 

[Mawa]

Doublade sin't an animal based desing.

Poochyenna, weepinbell, mewtwo

 

[Mawa]

Rhyperior don'T have a mega.

Flygon, Goodra, Charizard

 

[CoffeeDrink]

Rhyperior is the only one to evolve through trading. Further more, it's the only one that looks like a turd (has 'corn' pieces on its 'armour'), doesn't have a Mega Evolution, and the only one that should never have ever seen the light of day. Too slow, dang. My assessment of Rhyperior remains unchanged, however.

-Silly Goodra, you can't fly!
*Goodra attempts to Fly*
-That wasn't flying! That was falling, with style!

There is a number of ways this list could have gone:
Goodra is the only single typed Pokemon on the list.
Charizard isn't a Dragon Type.
Charizard if the only Fire type
Charizard is the only Flying type
Goodra doesn't evolve through leveling up alone (must be rainy in the overworld)
Flygon is the only one immune to Electric type moves
Flygon cannot learn Outrage etc.

This is fun.

My list: Girafarig, Igglybuff, Avalugg