Pokemon Locations

Here I'll give you the location(s) of some pokemon in certain games.
If you want to find pokemon by yourself then don't read further.
If any of the information is wrong, please report it to me.
If you are looking for a certain pokemon, hold Ctrl + F then type in the name of the pokemon and press find next to find that pokemon.

Mewtwo

Mewtwo can be found in Cerulean Cave at level 70 once you have defeated the Elite Four in Pokemon R/B/FR/LG.

Articuno

Articuno is found at Seafoam Island in Pokemon Y/R/B/S/G/C/R/S/E/FR/LG.

Zapdos

Zapdos is found at abandoned power plant in Pokemon Y/R/B/S/G/C/R/S/E/FR/LG.

Moltres

Moltres is found at Victory Road as well as Sevii Islands' Mt. Ember in Pokemon Y/R/B/S/G/C/R/S/E/FR/LG.

Lugia

Lugia can be found in the deepest cavern of Whirl Islands under the ocean floor only if you enter with a Silver Wing in Pokemon S/G/C.
Lugia can be found in Navel Rock along with Ho-oh in Pokemon E/FR/LG. To get to Navel Rock via a Seagallop Ferry you must have the Mystic ticket. This can be obtained by getting it transferred to the game at events such as the annual Pokemon Rocks America tours.

Regirock

Regirock can be found in the Desert Ruins after solving a puzzle in Pokemon R/S/E/FR/LG and Pokemon Colosseum and Pokemon XD.

Regice

Regice can be found in the Island Cave after solving a puzzle in Pokemon R/S/E/FR/LG and Pokemon Colosseum and Pokemon XD.

Registeel

Registeel can be found in the Ancient Tomb after solving a puzzle in Pokemon R/S/E/FR/LG and Pokemon Colosseum and Pokemon XD.

Latias

Latias can be found, in Pokemon Sapphire, in the wild after defeating the Elite Four but it keeps changing its location.

Latios

Latios can be found, in Pokemon Ruby, in the wild after defeating the Elite Four but it keeps changing its location.

Suicune

Suicune can be found, in Pokemon FireRed and LeafGreen, in the wild if your starter pokemon was Charmander.

Entei

Entei can be found, in Pokemon FireRed and LeafGreen, in the wild if the your starter pokemon was Bulbasaur.

Raikou

Raikou can be found, in Pokemon FireRed and LeafGreen, in the wild if your starter pokemon was Squirtle.

Kyogre

Kyogre can be found in the Cave of Origin in Pokemon Sapphire.
Kyogre can be found in Marine Cave in Pokemon Emerald.

Groudon

Groudon can be found in the Cave of Origin in Pokemon Ruby.
Groudon can be found in the Terra Cave in Pokemon Emerald.

Rayquaza

Rayquaza can be found in the Sky Pillar in Pokemon R/S/E/FR/LG and Pokemon Colosseum and Pokemon XD.