(emerald only) if you have a calm or modest ditto, and an everstone, you can give the ditto the everstone, and breed it with a ralts, and 1/2 of eggs will be calm/modest.
bold could work, as well, but only if you're using a set with W-o-W.
it'd be ok. but without having WoW to drop your opponent's attack, there's not much point in upping defense, because gardy's physical defense is only a little better than alakazam's.
any nature will work for beating the gyms, really. it's competitive/link-up/battle frontier that you have to worry about EVs and natures for.
yeah but I atleast want a beneficial nature that lowers attack (since it dosent use attack) and makes something useful a lil higher. And I may battle with friends, though i'm not sure.