The modern Pagan harvest festival named after a figure from Welsh mythology is Mabon.
Mabon is a modern festival observed by some Pagans and Wiccans around the autumn equinox. It is commonly associated with the second harvest, thanksgiving, balance, and the transition from summer toward winter.
The name was popularized in modern Paganism and refers to Mabon ap Modron, a figure in Welsh mythology. The festival’s name and many of its modern rituals are not evidence of an uninterrupted ancient festival tradition with the same title. This distinction is important because Mabon is often presented online as though it were directly documented as a pre-Christian Celtic holiday.
Modern observances may include shared meals, seasonal decorations, reflection, and gratitude for food and other forms of abundance. Mabon is sometimes called the autumn equinox, but the equinox is the astronomical event; Mabon is the modern religious observance associated with it.