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'M was one of the first Glitch Pokémon discovered, and, next to MissingNo., is one of the best known Glitches to this day. This is owed mainly to the fact that it and MissingNo. were the only Glitch Pokémon that could be found with the Old Man Glitch, which was discovered long before the Ditto Trick and other glitches.
There is much rumor and uncertainty surrounding 'M, which is common to any glitch of this sort. Many say that it will ruin your game cartridge, which may have something to do with the fact that it can scramble your game's graphics and Hall of Fame data. However, the Hall of Fame data glitch is easily overlooked, and the scrambled graphics can be fixed by viewing the stats of a non-glitched Pokémon, although they will return when 'M's stats are viewed. Though many claim that capturing a 'M and saving will delete your save file, this has not been confirmed by the Glitch City Laboratories staff. Many glitch researchers have captured a 'M with no permanent harm to their game beyond a glitched Hall of Fame.
The benefits of 'M are the real reason that people are interested in it, though. First, encountering one will give you 128 of the sixth item on your item list. This can be exploited to give you infinite amounts of any item in the game, without even needing to capture the 'M. Because the displayed item quantity can only go up to 99, the first digit of the quantity of the multiplied item will become a map tile, letter, or glitched symbol. Also, 'M has a massive attack stat and strange assortment of TM/HM learnable moves, although its pathetic Defense and Special make it largely unusable in battle.