@nellePoint It's a thing in a lot of old arcade games where, due to a bug (usually an 8-bit integer overflow), no further progress can be made. Either the level's impossible to finish, or the game outright crashes.
@nellePoint Indeed, they do require a lot of skill to reach, and they take a while to get to. I think my first Donkey Kong kill screen took about an hour and 45 minutes.