nowhere
(This question does not ask "which legendary is hardest to get.") I do not think that it is possible to say that anything that is legendary is more legendary than another something that is legendary. While some legendary things are more widely known than others, it does not mean that the first is more legendary than the latter. The point is, then, that there are no degrees of the word legendary.
rare there are more of. Legendary Pokemon there is ONLY ONE! hope that helped! :}
2 things there is more than 3 legendary Pokemon in the game and nothing is "unlocked" in the game if that is what you are asking
No, Espeon is not a legendary. It can breed with other Pokemon other than Ditto (It also belongs to an Egg Group) and it can be obtained more than once legitimately.
Any Pokemon can be the best depending on how you train it, the level, and the item it's holding. Though legendary Pokemon are more powerful than others, they still have type advantages and disadvantages.
It depends how legendary a Pokemon is. If its like diolga or palckia you only see them once.
Nah, Pokemon that you can get more than one of in games without cheating or trading aren't legendary in my book. I have heard someone call the Dragonite family legendary and Arcanine is actually called "The Legendary" Pokemon, but I think that's more for the TV-series.
Definetly. My friend has like 20.
Definitely not. If the Pokemon is available, you can use it. Though, to a certain extent, the use of legendary Pokemon can be wrong. If you have an entire party of legendary Pokemon, then it is wrong, since legendary Pokemon are much stronger than any normal Pokemon you could find more than once in the wild or any starter Pokemon. Keeping only one or two legendary Pokemon keeps the game fair. Think of it this way - if you were to battle a friend, would it be an unfair battle because he/she doesn't have that legendary Pokemon? Exceptions to the use of legendary Pokemon include the in-game legendary Pokemon, such as Lugia and Ho-oh in Pokemon HeartGold and SoulSilver (along with their respective Hoenn legendary Pokemon). Since these legendary Pokemon come standard, there isn't a reason not to use them. Pokemon such as Deoxys shouldn't be used, since Deoxys is more than extremely powerful and poses an unfair match for any other Pokemon, including some legendary Pokemon. In short, it is wise to keep only one legendary Pokemon that isn't from an event in battling others, but for the purpose of defeating the game, go ahead and use the legendary Pokemon. If Nintendo didn't want you to have such a powerful Pokemon, they wouldn't have created it.
Metagross is not a legendary Pokemon, for it can breed, it evolved from a previous stage, and can be found more than once. It is, however, considered a pseudo legendary, which is a fan-made term used for Pokemon with a stat total of 600.
If both of your Pokemon are legendary Pokemon you shouldn't take one of them out or else you cant put them back in. For instance if you are Giritina you cant put in another legendary in your team but you can put regular Pokemon in.
The best Legendary Pokemon with the best stats is none other than Mewtwo.