'M
'M (also known as "M Block") is a glitch Pokemon, much like Missingno, but is much more dangerous to your game. 'M looks just like Missingno, is the same type (Bird/Normal), has the same ID number (#000), has the same things happen to it (like not appearing in the Pokedex when caught) and like Missingno is only found in the wild in the Red and Blue versions. Yet it is not the same Pokemon. For example, it can evolve into Kangaskahn, which Missingno cannot do. 'M will evolve into Kangaskahn almost immediately after a battle, or with a rare candy. Even 0 experience points will evolve 'M. However, pressing the B button repeatedly will stop the evolution (just like with any Pokemon).
'M can mess up your hall of fame and duplicate your 6th item like Missingno, but catching it can result in freezing, game deletion, and/or permanant inaccessibility to Pokemon Stadium. Just like Missingno, 'M can be found by having a man with coffee show you how to catch a Pokemon in Viridian City, then flying down to Cinnabar Island and surfing along the east coast. There have been many rumors about 'M being able to evolve into Mew (Pokémon) but these are not true. 'M is also commonly refered as 'm block because of the letter "M" followed by glitchy boxes. It is also sometimes but rarely refered to as G.M.G. (Probably stands for Glitch 'M Glitch). Missingno. is almost always at level 100 or over, whereas 'M is always either level 0 or level 80. A level 80 'M can be sumonned by trading with an in-game trainer on the island, then surfing up and down on the coast. There are many theories of what 'M might be. some say that 'M was supposed to be the 4th legendary bird (which may explain why its type is bird/normal). Some say that it was Mew taken out of the game. Others say that it was a beta test like Missingno. 'M is much different than Missingno., and there are still many mysteries to be solved about Missingno and 'M.
If an 'M is taught a move like Fly and then is evolved into a Kangaskhan, the Kangaskhan will be able to use fly as an attack, which would not normally be possible. When the Kangaskhan that evolved from 'M uses fly in Pokémon Stadium, it will look like Kangaskhan is standing on air.