The Chain Game

Entei, a legendary dog! You know what, I like dogs!

Igglybuff, the cute little dude that eveolves into Jigglypuff!

Fenicchi Feraligatr, a cool alligator Pokemon!

Raichichi (Oh no! It's contagious!)

Raichu, the electric rodent that's always overshadowed by its prevo.

Umbreon, black cat, panther, dark, goldish, dull, thingy-ma-jigger

Numel, the derpy camel Pokemon.

Luxray, the epic electric wolf-thing.

Kingler, that Krabby (get it?) crab!

Ditto. That one made me think, I know there are more but I couldn't think of them.

@ShinyUmbreon
Well, there's always Dunsparce when you need 'im.
O, huh?

Onix, a nightmare for Pokemon Yellow players in the battle against Brock.

@ darkpokeball. That one is very hard cuz there is only 1 and that is Xatu.

Gardevoir, the pokemon in your avatar.
Wait...that's not creative enough.
You have a Mew in your signature.
I need a G.
The closest letter to 'G' in Mew's name is 'E.'
A pokemon whose name contains both 'G' and 'E' is Elygem.
Next person has a M.

Mewtwo. You mentioned Mew so I decided to say Mewtwo.

You mentioned two, so Porygon-2....wait.
I have to start with O...O2 is oxygen.
What pokemon relates to oxygen? Plants make oxygen so...
Grass Type!
Grass Type Pokemon that starts with O...
....
.....
Is there a grass type pokemon that starts with O?
Well, in that case, water is made out of H20. It has a 2 and a 0 in it. :P
So...water type that starts with O...
...
....
Are you kidding me? Not a single water type starts with O?
In that case, I've looked in Grass and Water. Both starter types.
The final starter type is fire.
Fire + O...
...
Wait. Just realized there are Water + O's.
Octillery, Omastar, and Omanyte.
In that case...which one?
Omastar and Omanyte are related, so that singles Octillery out.
Hence, Octillery.
Next letter is Y.

Yanmega. I think Yanma's evolution form is Yanmega?

Octillery, huh? So, next is a Pokemon that starts with 'Y'...

That's actually a tough one 'cause there are only three Pokemon whose name starts with 'Y'. But mate, I say Yanma!