What are the myths of Missingno?

One myth is that it's dangerous, which is also said of its cousin "glitchblock 'M glitchblock". Encountering them will most likely not delete your save data, but will unrecoverably mess up your Hall of Fame data.

Another myth is that it's left over from the developers quickly deciding to take Mew out of the game. This is not the case, because Mew is in the game.

Still more myths?