Remember Red and Dendrik? Well, this is the creature they came from. It's mass was so critically large, it split shortly after it crash landed on the planet. For reference sake, a normal person is about as tall as this thing is.

They can still merge to take this form. They cover each other's weaknesses, but adopt neither of their strengths. It's acidic, but lesser than red. It's malleable, but to a sloppy lesser degree.