A much simplified Celtic pantheon of twenty gods, goddesses, incarnations, and three Fairy Queens and two Fairy Kings are included below for use as the basis of the religious beliefs in my campaign setting The Kingdom of Delthos.
Major religious festivals include Imbolc, Bealtaine, Lughnasa, and Samhain. There are numerous local festivals as well, but PCs will need to observe or participate — in game — to know what they’re all about.
The Formorians are hostile and monstrous beings who come from under the sea or the earth. The people on the Borderlands of Delthos refer to Goblinkind by this name.
The Firbolg (men of bags) are said to be descendants of a people known as the Nemedians. The people on the Borderlands of Delthos refer to the native/aboriginal people who were pushed west of the Appella Mountains as Firbolg. As some of the PCs now know, one Firbolg tribe is the Hawk-Mu.
Áine na gClair is known in Delthos as a Queen of Fairy (na gClair = of the Wisps). She is the daughter of Manannán Mac Lir and an unknown mother. She also is known for her love affairs with human men and numerous clan chiefs in Delthos claim to be her descendants. She is associated with midsummer and the sun. She is sometimes represented by a red mare. https://en.wikipedia.org/wiki/Áine
Badb Catha (“Battle Crow") is an incarnation or aspect of The Morrigan who doles out judgment. Her cry causes terror in those who hear it and brings such panic that people fall on their own weapons or kill their comrades. "She can incite warriors into a heroic frenzy or terrify them into a panicked collapse.” Her personality is venomous, warlike, dangerous and deadly. Bringer of ‘mess’ (i.e. drunkenness and confusion). She can shapeshift into the form of a hooded crow. She has also appeared as a ‘washer-at-the-ford’ when she wishes to prophesy doom. Sometimes imbues a person with divine madness or crazy wisdom. https://geilt.com/spirituality/what-is-a-geilt. Also see http://searchingforimbas.blogspot.com/2007/12/geiltadecht.html.
Boann (Bóinn) is the goddess of the Lucky River (Ségda Sreb) in Delthos. Drinking from her river in June will allegedly grant the gifts of both poetry and seership. Cattle, especially white cows, are associated with her as well as the bird known as the oystercatcher. She is the mother of Óengus. https://en.wikipedia.org/wiki/Boann https://en.wikipedia.org/wiki/Oystercatcher
Brig (Brighid) is the protector and inspirer of poets and of agricultural fertility. She is a daughter of the Dagda and an unnamed mother. She had a son with the half-Fomorian King Bres. Imbolc is a holy day to her mid-Gillínmir (gelding month). Sometimes a small piece of cloth is left out on Imbolc eve which is then used in talismans of healing. Often she is invoked when Delthans purify or bless a new house or piece of land. She looks over rams, oxen and pigs.
Credne the ‘wright.’ Together with his brothers Goibniu and Luchta, he is a god of skill (Trí Dée Dána). Spear rivets, sword hilts, yield bosses and rims, silver arm.
Cliodhna is a territorial Fairy Queen said to be fair haired, shapely, and exceptionally beautiful. Her mother is not known, but her father was a Druid dedicated to the sea god Manannán Mac Lir. Several Delthan families claim descent from her, especially the King’s royal clan Mackay and the noble O'Keefes. Cliodhna can take the shape of a wren. She has three magical birds that eat Otherworldly apples and can lull people into a deep, healing sleep through their birdsong. She is passionate, and loves handsome bards who she may seduce (or drown if they offend her).
The Dagda the father-god in the Delthan pantheon, he is a larger than life, red-haired man with tremendous appetite for food and women. Also the master of Druidic magic, he possesses the cauldron of abundance from Murias (one city from which the Tuatha Dé Danann came), a great club that can heal or harm, Acien (ocean) the horse, and a harp whose playing changes the seasons. He can stop time. He is said to provide swift answers to prayers. He has many children and foster children. He is skilled at spying/disguise and at battle. Like most of the Tuatha Dé Danann, "he’s not just good, he’s good at it." (meaning many-skilled). https://en.wikipedia.org/wiki/The_Dagda
Dian Cécht is the ’swift traveler’ and physician to the gods. He possesses a cauldron (Slaine) which heals the wounds of those immersed in it. He helped King Nuada with his severed arm, Midir with his eye, and cures plagues and drives out serpents. He is brother to the Trí Dée Dána. He slayed his own son Miach out of jealousy of Miach’s healing skills. Herbal concoctions and oatmeal are offered to him.
Danu the mother-goddess, nature/earth goddess, and patron of female druids. She has also gone to battle and was one of the five goddesses who fixed pillars into the ground so that none of the Firbolg at the first battle of Moytura at Cong could flee the battlefield. https://en.wikipedia.org/wiki/Danu_(Irish_goddess) https://bardmythologies.com/danu/
Flidais is the slender goddess of milk and milking. She has soft hair and doe-like eyes. She is the mother of six children. She owns a magical cow that gives copious amounts of milk, and a combined herd of both cows and wild deer that likewise produce much milk with which she feeds people and armies. https://en.wikipedia.org/wiki/Flidais
Goibhniu is the god of smithcraft well known for making swords and spears of that never miss and always slay (although he himself is immune to this effect). Responsible for brewing the ‘fled Goibnenn’ a drink that can cure disease and extend life. Can heal wounds made with sword or spear. Owns a magical cow who gives an endless supply of milk. He is also architect to the fairies. https://en.wikipedia.org/wiki/Goibniu
Luchta the carpenter especially skilled in making spear shafts and shields. https://en.wikipedia.org/wiki/Luchtaine
Lugh the many-skilled spearman who defeated the Formorian Balor of the baleful eye. He acquired his spear by fulfilling a series of impossible tasks. Whoever has Lugh’s spear is said to never lose in battle. The festival of Lúnasa was founded by Lugh to honor his foster mother Tailtiu (a goddess of the Fir Bolg who helped them clear the land but died in the process). https://en.wikipedia.org/wiki/Lugh
Macha a goddess, patron of female Druids, a clearer / civilizer of land, a user of battle magic who helped send rain, fog, and showers of blood and fire on the Fomorians. She can shapeshift into the form of a crone or leper. The severed heads of warriors are sometimes offered to her and called Macha’s nut crop. She is (like Badb Catha) another aspect or incarnation of The Morrígan. https://en.wikipedia.org/wiki/Macha
Medb is a Fairy Queen who wears a red clock, has a bird or squirrel on her shoulder, and holds a flaming spear in her hand. She can run faster than any horse and the sight of her can deprive men of two thirds of their strength. She has a male harem she brought to the fairy realm, one of which is alleged to be her permanent consort. She occasionally grants mortal nobles a magical flag that can be used to call for aid https://en.wikipedia.org/wiki/Medb https://en.wikipedia.org/wiki/Fairy_Flag.
King Nuada and his wife Macha were said to have died in the second battle of Maige Tuired at the hands of Balor. Nuada owned one of the four treasures brought from the homeplace of the Tuatha Dé Danann - a sword which once unsheathed would allow the enemy no escape. Any wound from the sword could not be healed.
Oghma is one of the three champions of the pantheon along with the Dagda and Lugh. Ogma takes on one of the Formarian kings in combat, wins, and takes from him a sword named Orna which tells everything it has done when it is unsheathed. Ogma is the creator of the alphabet which bears his name to prove his ingenuity as a god of skill and eloquence. https://en.wikipedia.org/wiki/Ogma. https://en.wikipedia.org/wiki/In_Lebor_Ogaim
Óengus (Aengus) the god of youth, beauty, cleverness, and love. Has four white swans that circle his head. The festival of Samhain is of special significance to him. https://en.wikipedia.org/wiki/Aengus
Manannán Mac Lir the god of the sea. He has walked among fishermen as they repair their nets. Some islanders pay ‘rent’ to him at midsummer with offerings. He has a variety of foster children, but his daughter Áine na gClair is the apple of his eye (he has other magical apples as well). For him, the waves are as solid as land. He can control the weather. He has a special horse named Enbharr (water foam) whom he rides over the ocean waves. The fish are called his livestock. His enchanted sword, Frecraid (answerer) can slice through any armor. He also carries a golden apple branch as a wand that rings with a sweat music that can put people to sleep, or heal the ill and wounded. He has a cloak of forgetfulness that can take memories from a person, and a magical ‘crane bag’ that contains a variety of powerful magic items. He can creat realistic illusions and also has a magical boat. He has given gifts such as the féth faidha (cloak or breastplate) which can allow a person to become invisible and travel unnoticed. He keeps a herd of immortal swine and throws a feast in honor of the smith Goibhniu. https://en.wikipedia.org/wiki/Manannán_mac_Lir
The Morrígan is the war goddess and is sometimes called the queen of the dead, the phantom queen, nightmare queen, or great queen. She has sovereignty over the Otherworld. She has three aspects or incarnations (sometimes called her sisters) Badb Catha, Macha, and Morrígu. She is powerful in sorcery and has prevented escape of her enemies, and also confounded and weakened the Firbolg and Fomorians in their battles with the Dé Danann. She has turned people into water, terrified enemies, incited armies to fight by giving their leaders visions in dreams, and given many prophesies to her people’s warriors. She can take the form of a crow, eel, wolf, blackbird, a gray-haired crone and beautiful young red-haired woman. Once a year at Samhain, she is said to meet with The Dagda at a fork in a river to carry on a liaison. Others believe that she is the match of The Dagda and is his wife. https://en.wikipedia.org/wiki/The_Morr%C3%ADgan
Fionnbharr - Fairy King of the Dead - A benevolent figure who ensures good harvests, a master at chess (no human has ever beat him), strong horses, and great riches to those who will assist him. Onagh is his fairy consort/concubine. However, he also frequently kidnaps human women. https://en.wikipedia.org/wiki/Finvarra
Bodb Derg - son of The Dagda and a Fairy King. In the Acallam na Senórach, he was described as a handsome young man with long, golden hair and brown, two-forked beard. Bodb wore sandals of silver and his feet did not disturb the dewdrops on the blades of grass. Bodb is elected king of the Tuatha Dé Danann in the "Children of Lir", just as some of the Tuatha Dé are going underground to become the fairies/sídhe. The principle justification given for Bodb's election is that he is The Dagda's eldest son. Lir (Mannanan’s father) does not recognize his authority.