Missingno is not a pokemon, but a glitch. When you talk to the man who teaches you to catch a pokemon, the game changes the name, and stores all of the players information near cinibar island. You will be able to find missingno of any level there and depending on your trainer name, the other pokemon and their level. for example, if your trainer name is xDxBxA, you will find level 150 Mewtwo there. If you find a level 0 missingno, the sixth item in your bag will become 99 missingno, which means 99 million, so you can clone any item. If you catch missingno, it will mess up your game, and you could have trouble saving. Also, it might delete your hall of fame records as well as your pokemon. I read that on a website a while ago, but I forget what the website is.