No, not quite. An ultra ball should do it. Catch and/or use a Pokemon that knows Mean Look such as Golbat/Crobat. Then weaken Mesprit so you can catch it. If it faints turn your game off and then back on. Just make sure you have lots of ultra balls and potions (hyper/max/full restore).
A Master Ball
Mesprit or Cressalia. They are both running Pokemon, so they are very hard to catch.
jiroxy ball...
you have to trick it to come to you, then it will only stay with you for 1 turn so use a master ball.
use it any Pokemon that u have trouble catching u don't need it to catch mesprit or cresslina i used pokeball
The best ball to catch Deoxys is a Master Ball or a Timer Ball! Trust Me!!! Pokemon Master
You should use it on cresselia or mesprit because they run away
if you have a master ball catch it or if you have the move mean look
Use Electric Types To Paralyze The Get The Life Low And Use Ultra Or Great Ball.
Its hard, but try catching it at night when dusk balls work. hope this helps
A master ball
With a master ball but i would waste it on Mesprit!