The Heck² patch provides a collection of special levels to replace some of the maze levels in Gehennom. The new levels consist of fixed designs amid random mazes; the placement of levels into the dungeon is random. The patch is against NetHack 3.4.2 but also works with 3.4.3. The patch has a home page.
The patch makes extensive use of the des-file format, often ordering multiple MAP and MAZEWALK commands to produce the new levels.
There are five groups of Heck² levels: heck-a, heck-b, heck-c, heck-d, heck-e. Each game has a 25% chance of a heck-a level, a 50% chance of a heck-b level, a 75% chance of a heck-c level, a 100% chance of a single heck-d level, and four of the heck-e levels.
The heck-a levels include:
- Demogorgon escorted by two shriekers
- Dispater escorted by green slimes and disenchanters
- mind flayers and master mind flayers
- Geryon escorted by doppelgangers and werewolves
- iron bars and iron golems
- Yeenoghu escorted by minotaurs
The heck-b levels include:
- a cross-shaped level
- a room with many trolls
- a stream of lava with red dragons
- a maze of lava
- a dark, open region
- a small pool with kraken
- parallel, vertical corridors
- hidden closets
The heck-c, heck-d, and heck-e levels are less exceptional, but they insert open areas into the maze and sometimes unusual features like pillars or rounded rooms; they also insert solid wall, sometimes reshaping a level like 'm' or 'w'.
The biodiversity patch incorporates the Heck² patch. UnNetHack applies a modified version of the patch - some levels have been added to the mix, the numbers have been tweaked, and some of the least popular levels were removed.