First you have to get to the elite four and battle them then follow the monster face but DO NOT FLY! Unless you want to keep chasing it. Last have fun catching it.
No, you cannot catch Mesprit in either of those games. To get Mesprit you can:Trade over the GTSTrade from Diamond, Pearl, or Platnium
catch mesprit the lock for cresselia in base of mt.coronet
Mesprit Azelf Uxie Palkia
about three times but u can only catch it once
You fill up your pokedex then you will get national dex and all of battle island is opend and also you get to catch the other legendaires
Mesprit roams Sinnoh.
You can't, you will need to trade them from Pokemon Diamond, Pearl or Platinum.
Catch better Pokemon
if the Pokemon was mesprit, you need to chase him. on the pokewatch click the things until you find the map. there will be an icon that looks like a bear's face. follow the face. mesprit will be in the grass
Yes you can. later in the game Latias (or latios depending on which game you have) is attainable. Like mesprit in Pokemon diamond and pearl and like mesprit, latias and latios tend to flee.
you can catch mesprit after the championship on the wild >
First, use a Pokemon with mean look, such as Crobat, and use it on mesprit. DO NOT WITHDRAW YOUR POKEMON AFTER THIS! Next, attack Mesprit until it is ALMOST in the red zone. NOTE: If you attack Mesprit until it actually IS in the red zone, it will get panicy, thus making a catch nearly impossible. After you do this, either paralyze or put Mesprit to sleep. After that, get ready to throw LOTS of dusk and timer balls.