Endless Mode is a mode exclusive to Killing Floor 2 that was added as part of the Infinite Onslaught update. It is a variation of Survival Mode that allows players to participate in a (nearly) endless amount of waves.
Every fifth wave will feature a random Boss, after which the match difficulty will slightly increase. Even on Normal Difficulty you may see enemies use abilities and formations from higher difficulties once you reach the higher waves.
Enemy armor and shields scale much more harshly than health does, which makes the Patriarch the easiest boss in higher waves as he has neither. Conversely, Hans Volter and the Abomination become much harder as their shields and armor takes much longer to break.
During Endless Mode the Patriarch takes over as the Trader, and even has his own hacked version of the T.R.A.D.E.R. pods.
Despite being called Endless, the mode technically ends after wave 254, should you be able to reach that point.
Except during the first wave and Boss waves, you can also get a Special Wave. These can occur at the same time as a Stand Your Ground bonus objective. Special Waves come in two types: Outbreak and Specimen.
Outbreak waves feature the effects of a Weekly Outbreak for a single wave. Any Outbreak can be chosen except for Cranium Cracker or Zed Time.
Specimen waves are waves composed entirely of a single specimen. However, Specimen that were added to the game after launch do not have their own spawn pools and are instead programmed to sometime replace a different specimen. As such, those specimen appear in the waves of the specimen they have a chance of replacing. These include:
- E.D.A.R.: Appears in the Husk or Stalker waves
- Elite Crawler: Appears in the Crawler waves
- Gorefiend: Appears in the Gorefast waves
- Quarter Pound: Appears in the Fleshpound waves
- Rioter: Appears in the Clot waves
The amount of enemies that spawn during a Specimen Wave are modified depending on the Specimen (ie. for a Clot-only wave, a lot more enemies will spawn than normal, but for a Scrake-only wave a lot less will spawn).