They're very robust compared to normal norns. Their immune system is very powerful; they produce much more antibodies in response to antigens, and healing chemicals like Prostaglandin never decay. Furthermore, they're very resistant to wounding. They're naturally aggressive towards grendels. They are amphibious, as well.
They use ChiChi Norn sprites.
Notably, Autumn Norns need to be injected with the Creator or Agent Injector instead of the Norn Egg Layer or Muco. When injected, a single Autumn Norn will appear in the Norn Terrarium or Norn Meso alongside a storm of leaves. These leaves don't do anything except move around when a creature passes by and will eventually decay on their own.
The Autumn Norn genome was used as the basis for the Element Norns.