Flat mushroom-like plant
The pictures you sent in show a Bird's Nest Fungus, probably a species in the genus Cyathus. These small fungi grow and produce their fruiting bodies in mulch or in plant or wood debris. They are decomposers in our ecosystem, and are not harmful to people or plants. You can rake them lightly to break up if you want to remove them. They may come back every year, and are unique and interesting. If you look closely you may see the small egg-like structures down in the cup that are the spore-bearing structures. They are distributed by rain splash or animals. You can see how they got the name "Bird's Nest" fungi.
Here is a link to a fact sheet from UD Extension: http://extension.udel.edu/factsheets/artillery-fungus-and-other-things-that-grow-in-mulch/
Thank you for contacting Cooperative Extension,