Horde Mode is an expansion for Doom Eternal introduced with Update 6.66 on October 26, 2021. It is available to all players who own Doom Eternal or either of its downloadable content expansions, The Ancient Gods, Part One and The Ancient Gods, Part Two, even if they have been purchased as standalone items.
Horde Mode is presided over by Deag Ranak, who has devised a series of challenges intended to break the Doom Slayer. He will release "branded" demons into the battle at specific points and taunt the player if they run low on health.
Horde Mode is set across three levels - Cultist Base, Reclaimed Earth and The Holt. Each level consists of five rounds that take place in different locations across the level and are designed to provide a stern test of your combat and traversal skills. Every monster from Doom Eternal and its expansions is included.
- Arena - an arena combat encounter with multiple waves of demons. Rounds one and three will have two regular waves and one bonus wave, while round five has two regular waves and two bonus waves.
- Blitz - kill as many of one type of demon as you can before time runs out.
- Bonus Coin Round - collect as many coins as you can before time runs out.
- Traversal - use jumping, dashing and the super shotgun's meat hook to traverse the course and reach a portal. Collect as many coins as you can before time runs out.
- Bonus Blitz Round - same as the Blitz round, but with super-heavy demons, cueballs and Onslaught powerups.
When you start a new game in Horde Mode you can choose any difficulty except Ultra-Nightmare - this cannot be changed once the game starts. You begin with three extra lives and can collect more as you progress; if you run out of lives then the game ends and you must start again from the beginning. If you quit the game mid-level, you will restart from the beginning of whatever level you were on.
You start with only the chainsaw and a fully-mastered combat shotgun as weapons, but you will also have the blood punch, dash, a fully-outfitted equipment launcher and all Praetor suit perks, runes and Sentinel crystal upgrades. Another fully-mastered weapon is given at random each time you complete an arena round.
- The BFG-9000 is given at the start of Reclaimed Earth.
- The Sentinel Hammer is awarded when starting round five of Reclaimed Earth, but it requires four charges to use rather than two; picking up hammer charges will still fully charge the weapon.
A 3UP is awarded when you successfully complete a Blitz or bonus round, or a 1UP if you fail. Once you have obtained all the weapons, you will also receive a 1UP at the end of each arena round. A 2UP item can also be found in each Traversal round.
Points are awarded for every monster killed that is not a zombie, a mecha zombie, a wolf, a tentacle, a lost soul, a spirit or summoned by an arch-vile. Fodder demons award 50 points, heavy demons award 100 points, and super heavy demons award 200 points.
On wave two of each Arena Round (and wave three in round five), Ranak will release a number of "bounty demons" into the area - these demons are randomly selected and are indicated by a bounty symbol. The demons are initially highlighted gold, but after a while their value will decrease to silver and then bronze; if they are still not killed when time runs out, they will disappear and you will not be able to move on to the next wave. If you kill all the bounty demons in time then the final demon will leave behind a gold, silver or bronze Onslaught powerup - once picked up, this item will multiply all damage dealt as well as quadrupling, tripling or doubling all points scored for a short time.
In Blitz and Coin rounds, the monsters/coins initially have a gold value but will be reduced to silver and then bronze as time elapses. You need to kill the monsters or collect the coins as quickly as possible to score maximum points in these rounds.
Each level contains three combat challenges, which are derived from challenges found in the main campaign. Each challenge completed awards bonus points, and even more points are awarded for completing all three.
If you manage to complete Horde Mode, you will receive additional points depending on the chosen difficulty. You will also receive 1,000 points for every remaining extra life, and 50,000 points for never firing the BFG.
Every score that is obtained while online will be submitted into a global leaderboard. At the end of every horde mode season, all scores in the leaderboard will be reset, and items will be awarded to those who scored particularly high. It should be noted though that the leaderboard has a softcap - every score above and including 500,000 pts. will be automatically removed as it is deemed non-human. 
|Master of Turrets||Destroy an arachnotron turret.|
|Inflight Devastation||Kill 12 demons while in mid-air.|
|Disarmament||Destroy three arm cannon weak points on mancubi.|
|1||Arena||Arena after Station of Inquisition||Bounty demons are randomly selected every day.|
|2||Blitz||Cultist Key area|| Kill 12 pinkies in 60 seconds to unlock the Bonus Coin Round.|
Shoot the green overhead button to release swinging blades that instantly kill enemies.1
|Bonus 1||Bonus Coin||Basilica of Adjuration||Collect 20 coins in 45 seconds. A cursed prowler serves as an obstacle.|
|3||Arena||Station of Anointment||Bounty demons are randomly selected every day.|
|4||Traversal||Near Station of Inquisition||Collect six coins in 75 seconds and complete the course to unlock the Bonus Blitz Round.|
|Bonus 2||Bonus Blitz||Station of Inquisition||Kill 18 arachnotrons in 60 seconds.1|
|5||Arena||Slayer Gate arena||Bounty demons are randomly selected every day.|
|War Pinkies||Perform three different glory kills on pinkies.|
|Rocket Removal||Destroy four shoulder launcher weak points on revenants.|
|Keeping Cool||Use the ice bomb to freeze ten demons.|
|1||Arena||Office building past City Entrance||Two groups of bounty demons are randomly generated every day, and one of them is randomly selected for the round.|
|2||Blitz||The Chairman's Club|| Kill 18 Maykr drones in 60 seconds to unlock the Bonus Coin Round.|
Screechers will also be present - avoid killing them if possible.1
|Bonus 1||Bonus Coin||Upper Overgrown Offices||Get 20 coins in 45 seconds. Carcasses serve as obstacles.|
|3||Arena||Overgrown Offices||Two groups of bounty demons are randomly generated every day, and one of them is randomly selected for the round.|
|4||Traversal||City Entrance||Collect 15 coins in 75 seconds and complete the course to unlock the Bonus Blitz Round.|
|Bonus 2||Bonus Blitz||Reclaimed Train Stop||Kill 18 Dread knights in 60 seconds.1|
|5||Arena||Arena before Gate of Divum||Bounty demons are randomly selected every day.|
|Resurrect No More||Perform a "left-side" glory kill on an arch-vile|
|Angel of Death||Kill five Maykr drones with Precision Bolt headshots|
|Painkiller||Perform three different glory kills on pain elementals|
|1||Arena||Arena before Crimson Forest||Two groups of bounty demons are randomly generated every day, and one of them is randomly selected for the round.|
|2||Blitz||Launcher to Ivory Path||Kill 18 stone imps in 60 seconds to unlock the Bonus Coin Round.1|
|Bonus 1||Bonus Coin||Samur Maykr's arena||Collect 20 coins in 45 seconds. Tentacles and a Blood Maykr act as obstacles.|
|3||Arena||Slayer Gate arena||Bounty demons are randomly selected every day.|
|4||Traversal||Pit before Maykr Pillars||Collect 12 coins in 75 seconds and complete the course to unlock the Bonus Blitz Round.|
|Bonus 2||Bonus Blitz||Ivory Path entrance||Kill 18 mancubi in 60 seconds.1|
|5||Arena||Ivory Path arena||Bounty demons are randomly selected every day.|
- Changes with every season, so information presented here may be outdated.
Players' best scores are recorded on an online leaderboard, which tracks each difficulty separately.
Accumulating enough points in Horde Mode will also unlock cosmetic rewards from two different sets, "Classic Doom 2 Marine" and "Biker". Points are totalled across all Horde Mode games, they do not have to be gained in one session.
- The "Huge Guts" and "Comic Reader" rewards are based on the Doom comic.
- In the first season, there was a glitch where the bonus for not firing the BFG-9000 could be obtained even after firing the weapon twice - the player simply had to end the run full on argent cells. This glitch has since been patched, and cannot be used anymore.
- ↑ Boyle, Joshua (26 October 2021). "DOOM Eternal - Update 6.66 Release Notes." Slayers Club. Retrieved 1 November 2021.
- ↑ Boyle, Joshua (18 November 2021). "Update 6.66 Rev 1 Release Notes." Steam. Retrieved 16 January 2022.