The best way of catching a legendary is kind of hard, but here is something that will make it incredibly likely that you will catch it. First, save the game before challenging the legendary. Then, basically, you need to catch a weak Pokémon that can learn the move "endeavor". I think the only Pokémon in this game that can learn it at a low enough level is Starkly. It learns it at level 17. Make sure it never evolves. Give it a "focus sash". It will keep it alive with 1 hp if it gets hit with a move at max hp that would normally take it out. Next, make sure you have a Pokémon that can make it fall asleep, preferably 2 Pokémon with a move like that, as well as 2 Pokémon that can paralyze it. The moves that cause these status effects CAN'T BE DAMAGING MOVES. Depending on the type of Pokémon, where it is located, and the weather, you will have to make sure you have the right ball. An ultra ball is a very basic ball, it simply increases the odds. But there are others that increase the odds more dramatically depending on the Pokémon, the location, and weather. If the Pokémon is in a cave, you should have a dusk ball. If it is water or bug type, have a net ball. If it is a fast Pokémon, use the fast ball. But make sure that you have some quick balls at your disposal. If all goes according to plan, the Pokémon should be at 1 hp and asleep or paralyzed by the end of turn 3. After turn 4, the quick ball will go down to 3x the catch rate of a Poke ball. Use the quick ball on turn 4. If it takes more than that amount of time to paralyze it or make it fall asleep, restart from where you were before, right before challenging the legendary. Make sure you use as many effective bonus balls as you can before going to the ultra ball. It has only a 2x catch rate. Here is a link that can help you determine the odds of catching a Pokémon with that strategy with varying different balls: http://www.serebii.net/itemdex/ultraball.shtml I really hope this helps! It usually works, like 100% of the time.
The best way of catching a legendary is kind of hard, but here is something that will make it incredibly likely that you will catch it. First, save the game before challenging the legendary. Then, basically, you need to catch a weak Pokémon that can learn the move "endeavor". I think the only Pokémon in this game that can learn it at a low enough level is Starkly. It learns it at level 17. Make sure it never evolves. Give it a "focus sash". It will keep it alive with 1 hp if it gets hit with a move at max hp that would normally take it out. Next, make sure you have a Pokémon that can make it fall asleep, preferably 2 Pokémon with a move like that, as well as 2 Pokémon that can paralyze it. The moves that cause these status effects CAN'T BE DAMAGING MOVES. Depending on the type of Pokémon, where it is located, and the weather, you will have to make sure you have the right ball. An ultra ball is a very basic ball, it simply increases the odds. But there are others that increase the odds more dramatically depending on the Pokémon, the location, and weather. If the Pokémon is in a cave, you should have a dusk ball. If it is water or bug type, have a net ball. If it is a fast Pokémon, use the fast ball. But make sure that you have some quick balls at your disposal. If all goes according to plan, the Pokémon should be at 1 hp and asleep or paralyzed by the end of turn 3. After turn 4, the quick ball will go down to 3x the catch rate of a Poke ball. Use the quick ball on turn 4. If it takes more than that amount of time to paralyze it or make it fall asleep, restart from where you were before, right before challenging the legendary. Make sure you use as many effective bonus balls as you can before going to the ultra ball. It has only a 2x catch rate. Here is a link that can help you determine the odds of catching a Pokémon with that strategy with varying different balls: http://www.serebii.net/itemdex/ultraball.shtml I really hope this helps! It usually works, like 100% of the time.