How do you catch mesperit I try to fight him but he keeps running away..

Try to corner it and use your bike

Hope I helped!

Okay, get a level 40 or higher Haunter/Gengar that knows Mean Look, Hypnosis, [Ghost move], [Dark move]. Make sure it is night, and have at least 40 Dusk Balls. Now, save your game.

- Get in battle with Mesprit.
- Use Mean Look right away.
- Use the Ghost attack.
- If Mesprit's health is in the green zone, use the Ghost attack, again. If his health is in the yellow zone, use the Dark attack. If his health is in the red zone, use Hypnosis. If he faints, re-start your DS and repeat the above steps again.
- Once his health is in the red zone, use Hypnosis.
- Once he is asleep, start throwing Dusk Balls.
- If Mesprit wakes up, use Hypnosis again, and start throwing Dusk Balls again.
- Keep repeating the above statement, and you're bound to catch Mesprit, eventually.

Either use your master ball on it, or use an attack like block or scary face that prevents it from escaping. Then Put it to sleep/Paralyze/Burn/Poison. Slash Freeze.

The idea is not don't you use fly in battle, it is dont use it out of battle when trying to catch him (i think that is what you mean.)

Dont worry it may take a while, thats normal

Use a Pokemon with mean look, block, or Spider web. Use a Wobuffet too if you have one. Golbat and Gengar would both know it. Use mean look and wittle his Hp down, then throw ultra balls and dusk balls(night only). If you saved your Master Ball, use it. Mater Balls are meant for catching Pokemon that run away.