Koffing and Weezing are not obtainable in Pokémon X and Y so you'll have to wait for the release of Pokémon Bank and Poké Transporter on December 27th of 2013 to transfer one from any Generation V games (Pokémon Black, White, Black 2 and White 2).
Alternatively, you can ask a friend to trade you one or look for one in the GTS after this date.
Weezing does not evolve in Pokemon Ruby.
Yes You Can Get A Pikachu In Pokemon X and Y.
Weezing is #110 in the national pokedex, and it is a Poison type Pokemon.
Weezing can be found in Route 227 and Stark Mountain on Pokemon Pearl. Weezing isn't rare in the two locations it appears in.
The Legendary Pokemon available in Pokemon X/Y are:Xerneas (X only)Yveltal (Y only)ArticunoZapdosMoltresMewtwoZygarde
Pokemon X and Y are sold at MSRP of $39.99 (CAD)
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Prof. Sycamore will give you the oval charm in Pokemon X and Y.
Pokemon capable of learning Psywave as an Egg Move in Pokemon X and Y are Latios (Pokemon) and Gastly (Pokemon).
Koga's Pokemon are: Koffing Muk Koffing Weezing
I believe X is stronger, but Y looks cooler.
*Mew is not catchable in Pokemon x and y, but you can get him online from wondertrades and such. Mewtwo however, is catchable and you can find him in the cave in pokemon village.