How do you catch Mesprit once he starts running all over the map?

The easiest way to run into Mespirt is to run back and forth between two different routes. Each time you move to a new route, Mespirt will as well, so this is the best way to make him come to you, instead of you to him. There are lots of good places to do this. Just make sure the place you pick has grassy patches near. Avoid flying. When you use Fly, Mespirt will move to a random location instead of a bordering one like it will do when you change routes. It's confusing, but you get the hang of it pretty quickly.

As for actually CATCHING the little bugger, there are a couple of ways.

- The easiest way is to use your Master Ball. But keep in mind that there is another Legendary pokemon, Cressilla, who also runs around the map like this, so you can only use your master ball on ONE of these.

- Another way is to use a pokemon with the Arena Trap ability. This makes it so it cannot run away in battle. Wabbuffet and Dugtrio both have this ability. Conveniantly, when or if Mespirt DOES run away, it will sustain any damage that you do to it.

- Yet another way is to use an attack like Mean Look, which makes the foe unable to run away in the same sense that Arena Trap does. Tons of pokemon know this move, such as: Haunter, Golbat, Murcrow, Misdrevious, Duskull and Umbreon. Just keep in mind that if you switch out, Mespirt will be able to run away again. The same applies to Arena Trap.

Status ailments will also stay on Mespirt, which is good since putting it to Sleep or Paralyzing it will make catching it easier. If it faints, however, it's done for good and you will be unable to catch it.

Hope that gives you some options :)

If you get a Marking Map, you can get it.

This application can be obtained by speaking to the president of the Pokétch Company after obtaining your third badge. This application basically serves as a map of the Sinnoh Region. You can place icons on the map in case you get lost, etc. Mesprit and Cresselia (runaway pokemon) also appear on the map.

When you go to Lake Verity the second time, he will run away. You can track it using the Poketch Application. The easiest way to get him is to run in and out of Solaceon city until you both are in the same route, then go into wild grass. If youchave the music on, once the music starts you can tell if it's him or not becaus eh has different music.

Use any sleeping or block moves and weaken him and try to do this at night and use dusk balls becuase they are more effective than regular ultra balls. once he is down to a sliver and you meeet him try to throw some quick balls at the very first turn!

Well Good luck with Mesprit!

Try my technique by going from jubilife city to route 202 back and forth till you see misprit near I already have caught him.

you get a wobuffet and put him out front so that way mesprit can't run away