Phoenix Point's fourth DLC is due on October 1st. Corrupted Horizons adds a new corruption mechanic which can sap the will of your squad, as well as new Mutoid soldiers, pictured above. The Mutoids are immune to corruption, can learn any class's skills, but are unable to heal.
Corrupted Horizon's biggest new enemy is the Acheron, a four-legged strider that heefs corruption around a level. Units affected by corruption take a hit to their willpower, and as attacks stack your units can become unable to use some of their abilities.
Mutoids, meanwhile, are immune. Grown directly from Mutagens, one of Phoenix Point's resources, Mutoids are soldiers that can learn any class's skills, including those of the enemies you encounter. To counter that strength, they can select fewer skills at each level, reach max rank faster than humans, and are unable to heal when wounded.
The idea is that, as you progress through a game, you're forced to mix up your squad by swapping out corrupted soldiers for Mutoids with new abilities. For me, this kind of feature could go either way. I tend to get into a groove with a game and do the same thing over and over again. Features that push me out of that comfort zone can be great - or they can be a stressful thing stopping me from playing the way I was enjoying, and sapping my own will to continue.