Demons are largely associated with the judeo-Christian concepts of heaven, hell, god, and the devil. Angels abide in heaven with god, demons exist and are at the beck and call of satan, who was himself a "fallen angel."
There are many different versions of the tales from the Bible to the comic book characters Lucifer and Constantine. They can include spirits, succubi, incubi, seraphim, and cherubim. They can be human-like or monsters. The battle between good and evil makes for high stakes fiction.
Here is a list of questions to consider when crafting your angels and demons.
1. Where did their powers originate? Have they been around since time began or was there a point of origin? Are they the children of Eve, Lilith, God, Satan, etc.? Is there more than one type of angel or demon?
2. What is your construct of the story world? Are you basing it on the Judeo-Christian demons and angels or other mythology such as ancient Babylon, Inuits, native American lore, Buddhism, Islam, or Zoroastrianism?
3. Is a demon born or formed? What happens when demons or angels and humans reproduce, if they can? Can demons and angels reproduce with each other?
4. Are angels and demons immortal? If so, at what point do they stop aging or how do they age? Are they always born and made as adults? Do they physically age?
5. Can angels or demons be killed? If so, how and what happens when they die? Can they be banished from the earthly realm by a spell or ritual such as exorcism?
6. Do they have vulnerabilities such as religious icons or objects?
7. Are there costs associated with their powers? Is their energy drained? Do they need to "recharge" by some method?
8. What can your angels and demons do?
Control the elements of fire, air, water, earth
Grow or wither people, plants, or nature
Move things with the mind, wave of the hand, or incantation
Transport/teleport things or people
Telepathy
Mind control
Move through time and space
Kill, maim, or make others ill with their bite
Heal wounds, regenerate, or reanimate
Enhance senses: sight, smell, taste, hearing, touch
Superhuman powers such as excessive strength, speed, agility, intelligence
Shape shift
Fly
Powers of seduction
9. Do they reside only in heaven or hell and visit or can they live in the human realm?
10. Are there objects or rituals that attract them, bind them, or exorcise them?
11. Can they consume human food? Do they need any form of nourishment?
12. What is their hierarchy? Who do they answer to or do they have some autonomy?
13. Are they representative of a specific religion that binds them to codes of behavior? Are they bound by loyalty or vows?
14. Who sees them? Everyone everywhere? Certain groups or places? Only certain sensitive people or targeted individuals?
15. Do they have paranormal allies or enemies?
16. What do they look like? Do they have a supernatural appearance that is hidden by magic, spells, or glamours?
17. Do they have pointed ears, wings, tails, birthmarks, skin lesions, or tattoos? Are they short or tall? Beautiful or hideous?
18. Are their wings retractable or always out? What do their wings look like? Can they shape shift at will or is something required for them to do so? Do they become animals?
19 Do they have specific clothing, robes, armor, weaponry, jewelry items, etc.? What happens to their clothes if they shape shift?
20. Can they summon food, clothing, shelter, and other aspects of human living at will to appear human?
21. Are they battling for the fate of humanity or more distant observers who are not supposed to interfere?
22. Do they have specific tasks such as bringing the dead to heaven or hell or exacting reward or punishment on living humans?
23. What rules must they follow and what happens if they break them?
Further reading:
Worldbuilding: Myths and Legends
The Fantasy Skeleton
The Horror Skeleton
The Thriller and Suspense Skeleton
Demonology Wikipedia List
Demonology Jewish Encyclopedia
Deliriums Realm List of Demons
List of Angels and Fallen Angels
Hierarchy of Angels
You might also be interested in:
Story Building Blocks Build A World Workbook in print and ebook,
Story Building Blocks Build A Plot Workbook Fantasy in print and ebook
Story Building Blocks Build A Plot Workbook Horror in print and ebook
Story Building Blocks Build A Plot Workbook Thriller & Suspense in print and ebook
Fair folk are among the oldest of legends. In some lore, they are wise women skilled in the magic of the natural world. They have been associated with the elements of earth, fire, air, and water. In others they take the shape of winged sprites, elves, etc.
There are several well-known elements of fae tales: Shakespeare's Oberon, Queen Mab, and Tatania in A Midsummer Night's Dream, the summer and winter courts, seelie and unseelie courts.
Little people, or fair folk, include: fairies, pixies, imps, goblins, elves, gnomes, brownies, elementals, and other mystical people. Faery is sometimes an alternative realm existing separate from the mortal world.
Here is a list of questions to consider when crafting your Fae world.
1. Where did their powers originate? Have they been around since time began or was there a point of origin? Are they the children of Eve, a demon, or other god? Is there more than one type?
2. What is your construct of the fairy world? Are you basing it on the summer and winter courts, the seelie and unseelie courts, an alternative realm, or a place on earth hidden from humans?
3. Are you basing your fae on a specific folklore? What are the elements you wish to include?
4. Is one born a fae or can a fae be made? What happens when fae and humans reproduce, if they can? Can fae species reproduce with each other?
4. Are the fae immortal? If so, at what point do they stop aging or how do they age? Do they need spells or potions to prevent physical aging?
5. Can the immortal fae be killed? If so, how and what happens when they die?
6. Do they have vulnerabilities such as iron?
7. Are there costs associated with their powers? Is their energy drained? Do they need to "recharge" by drinking nectar or feeding off the energy, emotions, or dreams of humans?
8. What can your fae do?
Control the elements of fire, air, water, earth
Grow or wither people, plants, or nature
Move things with the mind, wave of the hand, or incantation
Transport/teleport things or people
Telepathy
Mind control
Move through time and space
Kill, maim, or make others ill with their bite
Heal wounds, regenerate, or reanimate
Enhance senses sight, smell, taste, hearing, touch
Superhuman powers such as excessive strength, speed, agility, intelligence
Shape shift
Fly
Powers of seduction
9. Do they reside only in Faery and visit or do they live in the human realm?
10. Are there objects that repel them or draw them in?
11. Are they reliant on food, nectar, or other nourishment to live?
12. Is there a hierarchy or controlling body such as a court, queen, king, etc.?
13. Do they have a religion or worship a god or demon?
14. If born a fae, especially in the human realm, do they live like normal human children and adolescents or are they sent to special schools or universities or have tutors?
15. Who knows about them? Everyone everywhere? Certain groups or places? Are they hiding in plain sight?
16. Do they have paranormal allies or enemies?
17. Are they an accepted part of society or must they hide in the shadows? Are they persecuted or the rulers? Have they infiltrated power positions?
18. What do they look like? Do they have a supernatural appearance that is hidden by spells or glamours? Do they have pointed ears, wings, tails, birthmarks, skin lesions, or tattoos? Are they short or tall? Beautiful or hideous? Are their wings retractable or always out?
19. Do they have specific clothing, ceremonial robes, jewelry items, etc.? What happens to their clothes if they shape shift?
20. Do they have familiars or control animals such as deer, birds, butterflies, or other animals?
21. Do they live and work like normal humans or do they have vast stores of wealth? If so, how did they come by it - magic or amassing human fortunes? Or can they simply summon everything at will including food, clothing, housing, etc.?
Next week, we look at crafting angels and demons.
Further reading:
Worldbuilding: Myths and Legends
The Fantasy Skeleton
The Horror Skeleton
The Thriller and Suspense Skeleton
Fairies
Celtic Fairies
Gods and Monsters: Fairy and The Fae
You might also be interested in:
Story Building Blocks Build A World Workbook in print and ebook,
Story Building Blocks Build A Plot Workbook Fantasy in print and ebook
Story Building Blocks Build A Plot Workbook Horror in print and ebook
Story Building Blocks Build A Plot Workbook Thriller & Suspense in print and ebook
A wide range of stories involve witches with unique traits and talents. Here is a list of questions to consider when designing your spell casters.
1. Where did their powers originate? Has witchcraft been around since time began or was there a point of origin?
2. Were they born with powers, gain powers at a specific age, or did an individual make a deal with a paranormal entity such as a devil, demon, or god?
3. Can anyone gain magical power? Are powers passed on through genetics, rituals, or other physical or mystical means?
4. Who can wield magical power, only certain individuals or is it accessible to anyone with the right knowledge or objects? What prevents other people from gaining magical powers?
5 . Once gained, can anything weaken or remove their powers? Do they have vulnerabilities?
6. Are witches granted immortality? If so, at what point do they stop aging or how do they age? Do they need spells or potions to prevent physical aging?
7. Can they be killed, even if they are granted immortality? If so, how and what happens when they die?
8. Are there costs associated with their power? Is their energy drained? Do they need to "recharge" or do they have an endless supply of magic? Does anything make them stronger?
9. Does using magic cause harm if used for personal gain? If white magic, what happens if they use it for nefarious reasons?
10. Is the magic available at will, channeled through specific objects, or energy drawn upon by spells, incantations, rituals, ley lines, etc. ?
11. What can individuals do with their magic and what are the logistics?
Control the elements of fire, air, water, earth
Grow or wither people, plants, or nature
Move things with the mind, wave of the hand, or incantation
Transport/teleport things or people
Telepathy
Mind control
Move through time and space
Kill, maim, or make others ill
Heal wounds, regenerate, or reanimate
Enhance senses sight, smell, taste, hearing, touch
Fly with or without brooms
Superhuman powers such as excessive strength, speed, agility, intelligence
Shape shift
12. Do they make potions? Is there danger associated with them?
13. Do they summon the power from a paranormal entity such as a demon or god/goddess?
14. Is there a hierarchy or controlling body such as a tribunal, coven, church, chosen leaders, etc.?
15. Do they have ancient texts, spellbooks, or grimoires? Interpret omens or magical objects like ouija boards, runes, bones, or sigils?
16. Do they have schools or universities? How are magical spells, potions, legend, lore, history, etc. taught or does the knowledge come instantly with magical powers?
17. Who knows about them? Everyone everywhere? Certain groups or places? Are they hiding in plain sight?
18. Do they have paranormal allies or enemies?
19. Are they an accepted part of society or must they hide in the shadows? Are they persecuted or the rulers?
20. What do they look like? Do they have a natural appearance that is hidden by spells or glamours?
21. Do they have special marks such as birthmarks, skin lesions, or tattoos?
22. Do they have specific clothing, ceremonial robes, jewelry items, wands, crystal balls, brooms, magical objects, etc.?
23. Do they have familiars such as cats or other animals?
24. Do they work like normal humans or do they have vast stores of wealth? If so, how did they come by it - magic or amassing human fortunes? Or can they simply summon everything at will including food, clothing, housing, etc.?
25. How do they live, like normal humans or do they have special homes or specific locations? Are their abodes visible or hidden with protections, wards, etc.? Can anyone approach or enter their home?
Next week, we look at crafting vampires.
Further reading:
Worldbuilding: Myths and Legends
The Fantasy Skeleton
The Horror Skeleton
The Thriller and Suspense Skeleton
You might also be interested in:
Story Building Blocks Build A World Workbook in print and ebook,
Story Building Blocks Build A Plot Workbook Fantasy in print and ebook
Story Building Blocks Build A Plot Workbook Horror in print and ebook
Story Building Blocks Build A Plot Workbook Thriller & Suspense in print and ebook.
Demons are largely associated with the judeo-Christian concepts of heaven, hell, god, and the devil. Angels abide in heaven with god, demons exist and are at the beck and call of satan, who was himself a "fallen angel." 
