In the Insanity edition of the game, challenge mode is an alternative game start accessible after choosing a character. There are two modes 'The Descent' places the player in an infinite Stonehenge dungeon, with the ladder leading to the next floor rather than the ritual room, while 'Challenges' offers a list of extra complications for complete runthroughs.
By default only the daily challenge is available and it will use the date to generate a playthrough with 3 handicaps and a single starting item that remain constant for the whole day, the required banishment ritual also remains the same through multiple games with the same character in the same day.
The other challenges each require spending a birth star to unlock and are identical to standard games except for the condition given on the screen when scrolling over the name. Most of these challenges are available for most characters and some are extremely challenging.