Out of depth

Most roguelikes generate monsters, traps, and treasure on a level based on the depth of that level in the dungeon (for traditional dungeon crawl roguelikes, however the basic concept applies to non-traditional settings as well).

Some roguelikes, Angband for example, will occasionally generate out of depth monsters and treasure that would normally only appear much deeper in the dungeon. This spices up the game with some exceptionally dangerous encounters that the player cannot plough through directly, but rather must exercise caution.