While it's technically not a fungus, I had my first experience with Fuligo septica, or Dog Vomit mold. My wife were gardening in the late evening and went inside as it got dark. About an hour later I let the dogs out and this yellow mass was in the mulch, probably about 6x5" in size. We assumed it was vomit from a racoon or something, but figured it out when it grew back the next day (in two spots this time). I would remove it every morning, but it would grow back for the entire week in different spots in the mulch. It was fascinating, but incredibly gross and kind of creepy!