Since I'm getting plenty of great for my other question "How can a nine tailed fox catch its prey?
Thought I might try to get ideas for both fox-fire and illusions.

So far I've thought of bioluminescent fungi which I called "fox shrooms" which are type of agaric fungus that glows a bluish-green in the darkness.

Here both the fox and the fungus share a symbiotic relationship which benefits both species, where the fungus lives on the dirt and decomposing matter often caked in the fox's dreads and as a bonus, the fox helps disperse the spores.     

But how can the spores help create fox-fire?