the chance of getting a shiny is about 1/8134 or something like that, i haven't checked in a while.
like the attack, hp, special attack, etc..
like.. when for instance.. im just picking a random pokemon
umm.. like pikachu.. if they normally get like 3 hp points when they level up, then when i give them the rare candy, they only get like 1 hp point or something..
it's kinda hard to explain.. so sry if it's confusing