To catch Mespirt you have to use the poketch app Pokemon tracker which you get from the poketch president after acquiring the veilstone badge. Using that you can track mespirt, i'd recomend flying to it until it ends up in an easy to track area. Then you just ride your bike or run until it is in the same area as you. Then you walk into the grass or water nearby and it should come up. Note: this only happens after the three legendary Pokemon return to their respective caves. Also, if you have a masterball of course that will make it easy to catch. I'd recommend chasing it with a high level Pokemon that has falseswipe to avoid killing it. I used my level 67 scyther but i had to chase it for awhile. You will only be able to throw one pokeball or attack the mespirt once, so i'd bring a Pokemon that also knows block like nosepass or another escape blocking Pokemon. I hope this helps and good luck.
you can catch mesprit after the championship on the wild >
luck
you use meanlook on him so he cant escape and you catch him
well you can catch dialga in diamond and you can catch palkia inpearl at spear pillar the only way to catch regigas is to catch the other regis you can catch them in plautim you can catch heatran at stark mountain you have to go there to times azulef mespirt and uxie are tough catch cresslia some where you have to get that marking map to get mespirt and cressila. Good luck. cheater
you go to all the caves in sinnoh (volar azelf acuity uxie and verity mespirt) and you will see them. battle them a try to catch them .But when you talk to Mespirt he will disappear .he will be roaming around sinnoh.
First go to a lake [not sure which one though sorry] and lower it's health and use a dusk, ultra or a great ball to catch it
for pearl catch palkia the main boss to pearl an go to the lakes verity valor acuity
You can find mespirt in : Dimond Pearl Platinum HeartGold Soulsilver Black 2 White 2 Pokemon Mysterdungeon Darkness/Time/ Sky (Maybe the new Mystery dungeon) (You may be able to catch mespirt in the new games, Pokemon X and Y)
go talk to the poketch app guy in jubilife city after getting your 3rd gym badge
You can find mespirt in a cave at lake verity. You can use surf to get to the cave. However, when you find it, it will go away. You will need to install an poketch app from the Poketch Company in Jubilife City. Then, the poketch app will show you where mespirt is. Although mespirt is very hard to encounter, once it goes to different places in the region, it's best not to use fly, instead, use a bicycle.
you have to beat the seventh gym leader then go to the spear pillar
I think you have to beat the eliete Four i know mespirt you catch in the wild use your mark map chart thing