Unlike Campaign, Horde Mode is rather self-contained, despite having to be played online. The player is spawned in an area covered in control centers, and has to spend a certain amount of waves defending control centers, and surviving. Unique to Horde Mode, if you are not revived before your revive timer runs out, you do not respawn until the next wave.
The player can beat Horde Mode by playing aggressively, or hanging back and working on crowd control.
As the player defeats enemies, acquires Wave MVP (multiplayer only), Turret MVP (multiplayer only) or flawless waves (no damage to the control centers), they earn Lien, which can be spent on buying turrets.
Turrets help the player defend certain locations, increasing their chances of completing the level. Players can purchase either machine gun, icethrower, grenade launcher or shotgun turrets, which provide various advantages and disadvantages to the battlefield.
Horde Mode is the only place where Mini Deathstalkers spawn.
Like Campaign, the more players are present, the more enemies spawn, therefore increasing the difficulty.
At the moment, there are 5 maps to play on for Horde Mode.
- Emerald Forest, 5 nodes over 10 waves
- Forever Fall, 3 nodes over 8 waves
- Mountain Glenn, 4 nodes over 10 waves
- Dr. Merlot's Island, 4 nodes over 10 waves
- Dr. Merlot's Laboratory, 4 nodes over 10 waves
- There is an unused and partially unfinished Horde Mode map for Dr. Merlot's Island in the game files (PC only). You can play it through gvk's mods, but players should beware as there are not a lot of invisible barriers to protect the players from falling through the map into infinity.
- The Horde Mode achievements are the most challenging to get, even though there are only 5 achievements directly related to Horde Mode.
- Turrets kills do count towards Rank requirements, except Turret MVP does not count as Wave MVP.