Is there a way to get good legendary Pokémon?

Question

I know ivs are random and you can ev train, but is there an easy way get a legendary Pokémon with a beneficial nature? I know you can't breed and wonder trading and the GTS is risky, so is there a method or are you basically stuck with what you have? (Example: I have a Timid Regigigas).

Answer 1

After you buy the appropriate Balls, you'll want to get a Synchronizer. "What's a Synchronizer?", you ask. Well, when you have a Pokémon with the ability Synchronize in the first slot of your party, all wild Pokémon have a 50% chance of inheriting the nature of that Pokémon. An even better trait is that the Pokémon doesn't have to be alive for Synchronize to work its magic, so you can have a fainted Synchronizer at the head of your party and the effects remain intact. This way, you can have an increased chance of getting the nature you want, which is something you'll have to decide on your own; which nature to use is a trainer's personal preference. Refer to the analyses in the Smogon Dex for ideas if you're stuck.
An optional Pokémon that you may wish to take with you is the "one under" Pokémon. This is a Pokémon that has a Speed stat one point below the maximum of the legendary you're trying to catch. This is for the Pokémon you really need to have reach a certain Speed. It isn't the wisest choice to bring one of these along for every legendary, since the "one under" Pokémon can be a pain to get, but it will be worth it if you don't have Master Balls. The idea is to switch your Synchronizer to the "one under" (or if your Synchronizer has been fainted just start off with the "one under"), then have the latter use an attack. If the legendary goes first, switch to the capture Pokémon and continue the battle, if not, reset. This "one under" should either be at a high level or holding a Focus Sash (which can be purchased from the Battle Subway or the Pokémon World Tournament).
If you are going for a defensive legendary that is not concerned about outspeeding certain threats or for a legendary you plan to use for a Trick Room team, you might wish to go for a different variation of the "one under" Pokémon that uses Endeavor. Endeavor is a move that takes the opposing Pokémon's HP down to the the Endeavor user's current HP, but it fails if the Pokémon using Endeavor has more HP than its target. This can be abused by giving your Endeavor Pokémon 1 less HP than the maximum HP of the legendary you are going for. If your "one under" Pokémon's Endeavor attack fails, you know that the legendary you are fighting does not have the amount of HP you are looking for, so you can reset without capturing it. If Endeavor takes the legendary's HP down, you know it is fine to resume trying to capture it. However, this Pokémon must also be faster than the legendary so that it does not risk taking damage, which would result in a false positive.

By the way, the "one under" Pokemon can also work with final gambit.
source