Mold

The car must have been in a dark damp place.
Dont dry brush the mold. The mold spores cause respritory problems, more so for the sensitive and /or allergic.
Tap water has clorine in it and will kill the mold. A little stonger mix of clorox and water with a sponge is what I would suggest. Then out into the sunlight and let the sun kill the rest of it.