"Folkbelief" mainly refers to the beliefs that various sociologists collected during the late 1800s. The motivation to collect this data tends to be nationalistic, ethnographic, whence "folk", and Romantic, in the sense of a reaction against the rationality of the Enlightenment. There is also a distinction between a "belief", which is mainly an eyewitness encounter with a paranormal phenomenon, versus a "tale" which is mainly a genre in the form of a complete story. The beliefs are understood to be true. The tales are often fictional elaborations of an encounter. While the 1800s typifies the kinds of phenomena that each folk encountered, the encounters themselves continued into the 1900s. I assume still happen today. I know Norwegians who are alive today who have seen a Troll, including Huldrefolk. Iceland too reports about analogous encounters. Normal sane people can have these kinds of experiences at some point in their life. (Personally, I make sense of the reallife reports of sightings, by associating apparitions of saints, ghosts, UFO encounters, nature beings, and so on, as a similar phenomenon that adjusts from culture to culture. I assume they are psychological subjective events but that are meaningful and informative for the wider community.)
The protagonist of the folk "tales" tends to be of a humble background. For example, "Ash-lad" and "Cinder-ella" are youth who daydream by the fireplace, while the rest of the family works ambitiously hard. It is precisely ones undervalued intuitive nature that allows this protagonist to navigate successfully thru realm of magic.
In folkbelief, magic tends to be ubiquitous, improvisational, and whimsical or strange. (This is also true in animistic worldviews generally. If you saw the tv series, Tales from the Loop, its sensibility seems remarkably animistic, despite it being a technological environment that is taking on a life of its own. Both hope and tragedy are part of the story of magic.)
If I recall correctly, Karl Jung in his cross-cultural (mainly Swiss) survey of tales about magic, describes a rule of three. One amount of magic is good. Two amounts of magic is better. But three amounts of magic is dangerous. Either the third use of magic will destroy the story and revert back to the original offering of the first amount of magic for some one else. Or else, a fourth amount of magic will save the day, rescue the hero, and accomplish the hopes of the hero.
For a D&D adventure story conveying folkbelief, it seems a helpful model to think of four big magical events, that the player characters eventually come across. The third one is a real challenge that can go very wrong. The fourth one often resolves the challenge in a surprising way, often according to the "morale of the story" − the ethical point that the story is making.
Improvisational magic is important in a folkbelief D&D setting. Similar to using Athletics/Acrobatics (a single skill I call Gymnastics) to do physical "stunts", I also use Arcana to do magical "stunts". Mainly, an Arcana "stunt" is an attempt to improvisationally modify a spell during spellcasting. For example, as a player, I modified a damage-dealing wind spell, to just do the wind without the damage, to push a crowd of bystanders out of the way of oncoming danger. If stunt failed, I could have seriously injured the crowds myself, but the stunt succeeded and they made it out safely. For us, Arcana uses whatever ability is the casting ability, whether Int, Wis, or Cha. Different approaches to magic approach magic differently, but equally competently. It is also possible to do a stunt to improvise a minor one-off cantrip-like effect. The DM determines the suitability and difficulty of a new stunt. I havent run into problems with spamming, but if I did, I would say, the same effect cannot be done twice in the same day or the same week, or for some effects, the same year or century. Using skill checks for stunts is a great way to for each character to employ magic improvisationally.
Folkbelief also has big magic, like floating cities, a queen giving birth to a draconic serpent, a grave becoming a portal into the realm of the dead, a sleep-enchantment broken only by the kiss of true love, and so on. For these kinds of story elements, use D&D rituals. Rituals can be almost anything. Rituals can have any effect and any requirement. Think of examples from folkbelief to determine the requirements of a ritual. For example, in one story, monarchs lack an heir and resort to magic to conceive. Finding someone who knows how to do magic is the first use of magic. Eventually this mage tells them to go to their garden and pick one white rose and one red rose. If they eat the white rose, their heir will lead their citizens in a time of great wealth, and if they eat the red rose, the heir will become a great conqueror of many nations. Wanting the best for their citizens, the monarchs eat both. They give birth to a serpent, a dragon, as their heir. For D&D, these are series of rituals.
A useful D&D spell is Mordenkeinens Magnificent Mansion. The nature being casts it by means of a "ritual". It allows player characters to enter the weird space of a nature being, like inside solid rock, or to enjoy a feast beneath the ocean surface. The esthetics of the Mansion are thematic, like ale that looks bluish clear like seawater with sea foam, dinner plates of fish and seaweed, and so on.
Folklore D&D 5e:
- Magic users are generally NPCs not players.
Folk tales rarely make the mage the protagonist. But it happens. In any case, the mages normally exist in the story, and the story can easily be about the mage, rather than about the warrior or the rogue.
Since the days of Gilgamesh into King Arthur, the jock has tended to be the hero of the story, not the nerd.
But stories like Harry Porter reflect a global shift in assumptions, making the technological Merlin archetype the center of the story, rather than the Arthur archetype.
D&D can and should encourage the mage to be one of the player characters.
And sometimes, the hero of a traditional saga or tale actually is a mage!
