Rare candy gives minimum effort values--meaning the Pokémon's stats won't increase as much when you level up. Just try battling naturally, and your Pokémon will have greater power than one that was just filled up with Rare Candies.
bidof raises hp, stary raises speed, golbat raises speed also, also their natures play a role in it 2, ex an adamant nature raises attack easilly, a jolly in speed and etc. gravelar n geodude raise defense, tentercal raises spc defense, n thts all i can remember right now
I'm no hero, the real heros won't be comming home.