Vegetative form is a bit of yellow slime containing many nuclei that crawls through the leaf litter eating microscopic spores, bacteria, dead matter, and so on. As it grows it becomes more prominent and forms a web of strands and lumps. When food runs out, or conditions change in ways not to its liking, it begins to produce the reproductive structures, called sporangia. First tiny yellow fingers begin to rise from the yellow mass. These later darken and develop into tiny nearly black grape-like structures on tiny pedestals. The grapes break down to release spores that begin new individuals.
Likes moist, shady wooded areas. Does not like bright light, from which it will flee. Occasional in the forested areas of Wildwood.
Dog vomit slime (Fuligo septica) looks essentially identical at some stages of its life cycle, but has very different reproductive structures. If found in the look-alike stages, the best way to distinguish them is by habitat. If it's out in the open in a sunny, exposed area it is certainly dog vomit. If in deep shady woods it is probably many-headed slime. Something similar but pink is probably the pink slime (Dicytdiaethalium plumbeum).
Many-headed slime is famous for its ability to navigate mazes to find food. It can also be used to create maps. Put food where you want it to congregate and shine light where you want it to keep out and it will produce a pattern of knots and strands that eerily mimic the US freeway system (knots = cities) or the Tokyo subway system (knots = stations).