Use a quick ball and hope- but if it doesn't work it will flee
it'll be in the grasses of sinnoh use meanlook + hypnosis then ultra ball
you put them to sleep or paralyze them
Yeah it is possible to catch kyogre with out wasting your masterball you wont have to use it until you see latias and latias requires you to use your masterball.
weaken it and put it to sleep
you can, the catch is fairly easy even without a masterball although I woul use ultra balls if you arent going to use a masterball. I you knock out reshiram without sAVing before hand you can try again after the credits at dragonspiral tower
A fleeing legendary pokemon
try using dusk balls
the strongest pokeball is the masterball. the masterball can catch any Pokemon out of the 493. it doesnt matter what kind of Pokemon it is, the masterball can catch any Pokemon.
Mesprit roams Sinnoh.
follow him (this is best done by switching in between 2 routes until he appears on one of them) and either use mean look on him or get him to the red zone with a status problem (preferably paralyzation) and use a quick ball or dusk ball at night until you catch him hope this helps XD
Mesprit Azelf Uxie Palkia
Use something like mean look to keep it from running, then catch it like you normally catch a legendary.