Keeper of the Seven Keys 3 (Disc One)

Keeper of the Seven Keys 3 - Disc One - is a six-level Doom II mapset for GZDoom created by David Newton (DavidN) in 2019 for the month-long NaNoWADMo event. It is based on the first disc of the concept album by German  band. The mapset features a techno-magic theme and primarily utilizes the OTEX texture pack, supplemented with some additional custom textures, including some Helloween-themed custom switches and banners. It also includes a modified version of Brutal Doom designed by DavidN, called "BDLite", designed to make Brutal Doom more streamlined and extensible (particularly for adding additional custom monsters and weapons).

Players begin the game in a hub map and can tackle the subsequent levels in any order they prefer. Each level starts from a pistol start, there are no carryover items besides the seven keys that the player must collect in each level. Most levels feature a map-specific gimmick and take inspiration from the song they are titled after. Each level contains one of the seven keys referred to in the album title and the level ends once the player obtains the key.

Difficulty settings
The WAD features three custom difficulty settings:
 * Tourist is lowest skill level and is for people who don't like fighting. Players only take 10% of the damage from hits and monsters have only have 40% health.
 * Apprentice applies small damage and monster health modifiers like the previous skill level. Players only take 60% of damage from hits and monsters have 70% health.
 * Kepper is the default skill level and features no applied modifiers.

Soundtrack
Each level features MIDI renditions of the songs they are based on.
 * MAP01: "The Keeper of the Seven Keys"
 * MAPA: "The King for a 1000 Years"
 * MAPB: "The Invisible Man"
 * MAPC: "Born on Judgment Day"
 * MAPD: "Pleasure Drone"
 * MAPE: "Mrs. God"
 * MAPF: "Silent Rain"

Custom monsters
All of the default Doom II bestiary is replaced with their Brutal Doom counterparts. In addition to those monsters, the mapset features the following custom monsters:


 * Zombie fodder
 * The first enemy you encounter is this lowly, low-tier monster with a melee scratch attack. It has 15 hit points.


 * Zombie scientist
 * There are several different variants of the zombie scientist, most having 20 hit points and a melee attack (crowbar, sledgehammer, axe). However, there is a more deadly plasma-shooting variant that has 50 hit points.


 * Sound-sensitive turret
 * Mechanical turrets that activate when alerted by sound, firing a devastating constant hitscan attack that can only be broken by getting out of its line of sight. These turrets feature prominently in MAPF: Silent Rain.


 * Invisdemon
 * A demon variant that is completely invisible and can only be detected by the splashes it leaves behind when running through liquids. This monster features prominently in MAPB: The Invisible Man.


 * Pleasure drone
 * The titular monster from MAPD: Pleasure Drone, this is a cybernetic baron of hell variant that shoots a health ray at the player, restoring their health. While this monster mostly functions as an ally, the player cannot let it get too close as it will still try to do damage to the player with its melee attack.


 * Mega mastermind
 * A stronger variant of the spiderdemon that serves as the boss monster for MAPE: Mrs. God.

Custom weapons
The mapset replaces all stock weapons with those from Brutal Doom. New weapons are listed below.


 * Keeper staff
 * This is the default weapon, replacing the fist. It allows the player to use a weak jab melee attack.


 * Assault rifle
 * This replaces the pistol and is taken from Brutal Doom. The player does not start with an assault rifle and must find one in the level to use it.


 * Minigun
 * This replaces the chaingun. Like most of the weapons in this mapset, it originates from Brutal Doom.


 * Grenades
 * Grenades serve as an alternate firing modes for all weapons.


 * Flak cannon
 * The flak cannon shares the weapon 7 slot with the BFG9000 and is taken from Brutal Doom's weapon of the same name.

Trivia

 * The text message after beating the mapset is taken from the spoken word intro to "The King for a 1000 Years".