Were can you get a MissingNO?

Answer 1

I will tell you how to get Missingno, but be warned, the Missingno glitch if done enough times can corrupt (mess up) your save file, and occasionally (but very rarely) your entire game.

To get Missingno, first you go to Viridian City and talk to the old man who teches you how to catch a Pokemon. When he asks if you want to see how to catch a Pokemon, say yes. After he's done showing you, fly to Cinibar Island and and Walk to the East (right), when you get to the edge of the island, surf up and down the side of the island. Be very careful not to go right any further, go back on land, or leave the side of the island in any way (if you do, start the glitch over). You should start to see Pokemon of all kinds, and most of them are going to be over lvl 100 (If you don't want you're file to corrupt, whatever you do, DO NOT CATCH THEM). Then eventually you'll run into Missingno, (or a commonly seen form of Missingno, known as "M"). If you want to catch Missingno (which will lead to very quick file corruption if done succesfully) then I just want to let you know, it can break out of a master ball. Also, whatever item you have in your 6th spot, will be multiplied by over 100 upon encoutering Missingno (I often use it with rare candies or master balls).

I hope this was helpful!