The extra difficult Secret Levels that some games have. They exist largely so that the player can brag to his friends about how awesome he is for winning them. A subtrope of Secret Level, distinguished from its mother trope by the fact that the extreme difficulty is pretty much the only point of these levels. Examples of this trope are, naturally, almost always That One Level. The idea appears to be that if you're good enough to get there, you're good enough for whatever the game decides to torture you with. For the boss version of this, check out Bonus Boss, or alternatively, True Final Boss.