Marsh Land/ Swamp Biome.

[Elixiar]

Rain is very common, land is inconsistent making building larger structures difficult and irregular.
Trees grow faster, making wood dominant resource (A lot of rain means your base won't be too easily razed to the ground but still completely possible.
Mysterious Blights are much more likely but wildlife is everywhere - however swampgators attack if a colonist gets too close and can take off a limp easily. (Taking advantage of new allowed areas)

Since this isn't Earth could add some tiny Low-glowing flora or ambient fireflies to lake nighttimes pretty.

Want a biome like ice sheet and desert for difficulty but in the neutral ground temperature region. Lack of consistent land to build on (marsh patches) swampgators and slow movement speed are the main enemy in this biome. As opposed to scorching heat or lethal winters!