Shiny pokemon are some of the rarest things in the world of pokemon and the chances of randomly encountering a shiny pokemon stand alongside the ranks of obtaining a pokemon with perfect ivs and a pokemon getting sick with the pokerus. Shiny pokemon are, of course, a different colored variant pokemon. A "shiny" pokemon exists for each regular pokemon and are encountered either in the wild or through breeding, evolution will obviously not change a pokemon from shiny to regular or vice versa. During GSC, when shiny pokemon were first introduced, the odds of finding a shiny pokemon were 1 in 8,192; or a 0.0001220703125 % chance of encountering a shiny pokemon. During GSC shiny pokemon seem to have been determined by whether or not a pokemon had a particular iv spread; and thus a number of different particular Iv spreads resulted in that pokemon being shiny. As of RSE the calculation was changed to use both a player's trainer ID number and personality values (4th generation), to determine whether or not a pokemon would be shiny. As a result of this new calculation, the chances of encountering a shiny pokemon were changed to be 2 in 65,025; or a .0000307574009 % chance. Slightly worse chances in the latest generations, it would seem. Shiny pokemon are really not much more than a collector's item and a fun addition to the already extensive list of possible side quests, as even at their best, shiny pokemon do not offer any additional bonus for obtaining them (better chances of getting higher Ivs, etc.)
While breeding does not increase the chances of getting a shiny pokemon (breeding 2 shiny pokemon together still results in a 2/65025 chance) Perhaps ironically, some of the rarest pokemon actually have a better chance of being shiny pokemon, or any pokemon which you would be able to apply a soft reset to (act of saving the game right before battling a pokemon, such as dialga or palkia, and then turning the game off and then back on if something went wrong during the ensuing battle against the legend). The act of soft resetting allows you to continue to play against a wild pokemon multiple times. Soft resetting is most often used for getting good IVs on a pokemon, but can be used just as effectively to obtain shiny pokemon. A reminder of course, soft resetting is useful in and of that the alternative to soft resetting would be to attempt to siphon through other wild pokemon in an attempt to reach the pokemon you were trying to get a shiny version of. Soft resetting does not decrease those 2 in 65,025 chances.
Currently the only available method of identifying a shiny pokemon in the wild is through the use of the pokeradar which will emit silver sparkles in the grass if a shiny pokemon is in one patch of grass. Another method, chaining, used with the pokeradar, is also effective in obtaining shinies as when you see the same species of pokemon, with the pokeradar, in a row, it essentially provides the same opportunity as a soft reset; though I have heard some claim that seeing the same species of pokemon in a row, with the pokeradar, actually increases the chances of seeing a shiny pokemon, though I cannot confirm that. (Comment below, if anyone knows.)
Various nintendo and other events, where they give out pokemon, have had shiny pokemon confirmed to be given out at them.
- Among shiny event pokemon that were given out at events, pokemon with the OT10 ANNIV and 10JAHRE have been confirmed to have been given out as shinies.
- Mew's with HADOU, MYSTRY, and Aura OTs have been given out as shiny, but Pal City has not.
- Jirachi's with WISHMKR and CHANNEL OTs can be shiny, though Wishing Star has not.
- Ho-Oh's with a MATTLE OT have not been given out as shiny.
- Any of the 3 Regi's with the HADOU OT (ID# 50901) can be shiny.
- Deoxys with the SPACE C and DOEL OT have been given out as shiny.
- No Manaphy's from Pal City were given out shiny, but Pokemon Ranger did have that capacity.
- Darkrais from the movie were not given out as shiny either.
- Pikachu's with the PKTOPIA OT do not seem to have been given out as shiny.
- Both Magma and Electabuzz with the FESTA OT can be shiny.
- Wishcashs with the YAMAMOTO OT were not given out as a shiny.
- Lucarios with the PALCITY OT were given out as shiny, though it sounds like many of them were hacked and thus caution should be used when trading for one.
- Concert Chatots had shinies given out.