Horde Mode Guide

A guide for beating horde mode. After trying the first six waves a couple times, I got a feel for it, planned out a strategy, and finished it on Exterminatus on my first try.

Introduction

My guide shows two of the secrets. Check this guide for the rest of them:
https://steamcommunity.com/sharedfiles/filedetails/?id=3337175761
Check this guide for what the blessing of the Machine Spirit does for your holy wargear:
https://steamcommunity.com/sharedfiles/filedetails/?id=2982526848
I blessed my Bolter early on. It's ever-reliable at all ranges against most enemies and you won't be handicapping yourself while you grind through rounds to get access to other weapons. Your mileage may vary depending on preference, etc.


Be sure to run around the map to grab health/contempt/ammo/grenades between each round as all these normal pickups respawn at the start of each round (exception: they do not respawn at the start of round 1). Grav-Cannon and Heavy Bolter ammo are especially important not to miss early on as it will take multiple rounds to max out your ammo.


-The first round is just cultists.
-The second round adds basic Chaos Marines to the cultist hordes.
-The third round adds a Terminator and Aspiring Champions.
-Rounds four through six are Nurgle-focused. Cultists and Marines still show up. A Great Unclean One appears in round six.
-Rounds seven through nine are Tzeentch-focused. Cultists and Marines still show up. A Lord of Change appears in round nine.
-Rounds ten through twelve are Chaos Undivided. Of special note is the large number of Aspiring Champions in round eleven. They can be especially dangerous depending on where/if they catch you. A Sorcerer will appear in the last round.
-As you're moving into the exit hallway, a lot of Nurglings spawn by the exit door.


Pick up the Bolter in the middle of the second floor to start purging heretics!
(there will be a new thing to pick up here between each round)

Tips

At the latest, between round 1 and 2, run through all the summoning circles (there are several around the map, the following screenshot is an example). Some will spawn a Blue Horror or Nurgling and it's best to set these traps off when there's nothing else going on so you won't get surprised later. It is random which will spawn a daemon and the traps do not reset.



Rounds will often end without you having killed every enemy. There will be stragglers to mop up between rounds. Use the pause menu to check if you've slain everything.


A Vortex Grenade (plus the other rewards for the round) is available in each room that the three keys unlock. You get a key after every third round. For the red room (grabbing the red key starts round four), rush in, grab the Heavy Bolter and Vortex Grenade, and rush back up to your base on the 3rd floor. Do the same with the purple key after round six (you grab a Volkite Caliver and Vortex Grenade this time). The yellow room (the relevant key is the reward for finishing round nine) has a Munitions Boon, Infinite Ammo, and the last Vortex Grenade. You may find that skipping this room until after the round is over is better than going for it and having to cross back over to the third floor base, but the Infinite Ammo with the Grav-Cannon will cut through a lot of enemies (and make it easier to cross back to relative safety).


Make sure all weapons have been reloaded before picking up the Munitions Boons. Boons do not refill magazines, they only max out what you're carrying.


For the various other temporary powerups (special Bolter ammo, Assault Doctrine, etc.), use them as you see fit. I found them to be unneeded, although the special Bolter ammo is always useful as they're just extra damage and extra ammo.


Rebind the keys to more easily access your Meltagun and Grav-Cannon. Scrolling through all of your guns or reaching for the 6/8 is inconvenient. These two put out a lot of damage, aren't a danger to yourself, and can reliably get you out of a pinch (like when a Champion is charging at you).


Aspiring Champions can fully revive if you don't gib their corpses.


Leave as many +2 health/contempt pickups that dropped from enemies around the map as you can. Top yourself up to 200/200 with the +100 pickups from the crates scattered around (more of these open as you finish rounds) then focus on using the respawning +2 pickups. You may find it useful to mix it up though and leave some of these respawning pickups so that there always some to grab in any area of the map in case you end up running around more than expected.

Make Your Stand

On the third floor, at the end of the walkway by the stack of crates, face the blocked exit door, and look up and to the left. Shoot the skull. This unlocks one of the crates behind you.



You will hole up in the crate that opens up for most of the run. Ranged enemies are the main threat of course. This is especially true of any heretics wielding plasma weaponry because of the AOE and Pink Horrors as their fireballs can track you to a degree. Screamers can't get in and Bloat Drones won't shoot in.



Enemies can pile up right outside the crates below your view (nurglings, lesser toads, and cultists in my experience). You can clear them out without being seen by them by hitting the railing and column with plasma rounds or explosives from the Vengeance Launcher. Be careful about hitting the geometry of the edge of the crates though, especially with plasma.



After using the red key, the crate below the secret crate opens up. Save the health/contempt in this one for when you're in a pinch during a round so you don't have to travel far.



A note about the boss fights; you will need to leave the crate to do battle with them. In my runs, I was never aggro'ed by them while in the crates. For the Lord of Change and Sorcerer, you can safely wait until you've killed most/all the other enemies before exiting the crate, but keep in mind that the Great Unclean One will keep spawning Nurglings. A final note about the Lord of Change; in my runs, waiting long enough in the crate resulted in it stopping somewhere in the map and it would no longer teleport. It wasn't hard to find places to shoot at it where I'd be out of its line of sight because its vision was obstructed, but I could see (parts of) the rest of it.

The Ambulls

Open the secret door (this is just forward of where you spawn) and run off so you don't catch their aggro (which is based on line of sight, you can walk right up behind them if they haven't seen you and you don't already have their aggro). These guys are beefy and, as neutral enemies, they'll also fight the chaos filth. Earliest I'd let them out is to fight in the 3rd round which starts with you grabbing a Plasma Gun. (I let them out in the 5th when I did my run)



They will return to the spot right outside the secret room they originally come from when not fighting. Between rounds, finish them off so that a new set will spawn at the start of the next round.