Instructions
Catch a Pokemon that has the abilities Block or Mean Look. Both abilities, when used, make a Pokemon unable to flee the battle. Some Pokemon that learn these abilities include Snorlax, Nosepass, Bonsly, Zubat, Haunter and Umbreon.
Press "Start" on your Nintendo DS and select "Pokemon." Place the Pokemon that knows either Block or Mean Look in the first position in your lineup. This ensures that this Pokemon is the first Pokemon on your list to enter the battle.
Locate Mesprit and engage it in battle. The location of Mesprit is noted on your map but changes randomly as you play. Walk in the tall grass on the route Mesprit is located in to engage it in battle.
Use the ability Mean Look or Block as your first attack. Your Pokemon uses this move before Mesprit has a chance to attack, stopping him from fleeing. However, if you switch Pokemon or that Pokemon is defeated, Mesprit can run away again.
Use your strongest moves and abilities to lower Mesprit's health. When its health bar, located underneath his name, is red, use a Pokeball to capture Mesprit.