Fae

The fey are not a singular species, but a set of beings that have been changed by the influence of chaotic and life energies drawn from the outer planes.
This definition is not wholly accurate, however, because some entities would be better described as tangles of chaotic energy mimicing the forms of beings familiar to us in the material plane. For many fey, there is no telling which category applies.

Feywild

The majority of fey are associated with the feywild, a vast mirror-demiplane of the world, where life is lived faster, richer and more briefly. It could be said that the feywild itself is a fey entity, mimicing the natural realm and growing vast and complex on the life energy and chaotic magic it channels.

Seldarine

The gods of the elves were originally powerful formless chaotic beings rumoured to have travelled to our realms through planes of pure chaos. When they arrived, their leader Corellon created the progenitor fey race, including the elves. As time passed, the elves settled into their humanoid forms and lost their polymorphic heritage, and the individual members of the Seldarine settled into the roles and responsibilities of divinity. By consensus, they chose to follow the elves and solidified their common forms into ones resembling their mortal children.

Fey wildlife

Many fey creatures are similar to ordinary beast but warped by magic and chaotic power. Some develop unusual intelligence or magical ability, while others take on or mimic the shapes and aspects of other beasts.

Sprites

A common form for intelligent fey life is to be small humanoid and winged. Pixies often use size-changing magic to interact with people on equal height terms. Griggs are musical sprites and have the lower body of a cricket.
Other sprite-like creatures mimic other forms. A good example is the faerie dragon, which is a tiny creature that has the draconic body, but beautiful butterfly wings.

Humankin

Both elves and gnomes are said to have originated in the feywild. Trolls and goblins are said to have started as some mad deity's mimicry of elves and gnomes, and goblins, hobgoblins and bugbears still retain some fey ancestry. Some giant-kin with particularly nature-aligned or chaotic inclinations, like firbolg and formorians were considered to be partly fey. Many of the elves that remained inhabitants of the feywild slowly absorbed the seasonal fey magic of their surroundings and became eladrin. The most powerful elf-like beings, or the powerful beings that used elf-like forms, are the archfey or fey lords. They attune with magic to embody a concept or principle and draw immense power from the symbiosis. The courts of the fey are ruled over by the kings and queens of summer (fire, growth, happiness), winter (air, darkness, cold, hunger and the hunt), autumn (earth, harvest, decay), and spring (water, hope, mischief),
Many creatures are changed over time by the savage and predatory nature of some fey power. Redcaps are goblin-like beings who delight in spilling blood and causing harm and use magic to assist them in that. Hags are fey creatures who usually take the appearance of old women. They delight in the misery of others. Many hags build a reputation of providing aid to those who seek them out, only so that they can turn the desires of others against them, providing a cure but at a cost that causes even greater harm, or fulfiling a wish in a way that causes them to regret wishing it in the first place. Hags generally take on aspects of their surroundings. Sea hags develop moist blue-tinged skin dotted with barnacles and grow kelp-like hair. Green hags live in forests, with green skin and scraggy hair, but would usually use illusion to appear as an aged sorceress or witch. Bheur hags from the cold north grew pale and skinny, wearing big cloaks of fur. A certain breed of hag, known as Night hags, migrated to the negative outer planes and became fiendish in nature. They posessed darker skin and worked magic through sleep and nightmares. The most fearsome and oldest hags slowly become what is known as an Annis hag. Their magic expands to warp and shadow their surroundings, their bodies expand with unnatural strength, while their teeth and nails turn to sharp, rusted spikes of metal.

Changed beasts

Owlbears and blink dogs are both considered native to the feywild. Confusingly, some beings with celestial origins, like unicorns and pegasi, find homes in the feywild but are not considered fey in nature. Intelligent versions of natural beasts, and those with additional magical power, often have connection to the feywild. The harengon, intelligent humanoid rabbitfolk, have recently been encountered more often on the material plane.
Satyrs and centaurs, along with other creatures mixing humanoid with beast may originate or find home in the feywild.

Shadows

The fey energies of change and illusion make it useful for creatures who love darkness. Sometimes merely secretive, like the brownie or brigganock, other times influenced by the darker side of life, like the meenlock or yeth. The boggle is a creature of stealth and escape, and the dark oil excreted from its skin is frictionless (and psychoactive). The yeth is a shadow hound excelling in hunting. The meenlock is a gremlin that feeds of the fear and despair of its trapped victims. The brigganock is a tiny humanoid creature that mines the rocks of the feywild for the magic left there by mortal dreams and wishes. Many of these creatures can slip between the material, the fey and fell planes wherever a suitable gap can be found.

Nature spirits

Many semi- or non-corporeal spiritual lifeforms take humanoid shapes (particularly when interacting with humanoids). Dryads are the coalesced spiritual awareness of a tree or forest, and while some are not reliant on a particular tree or location, none can survive without the close connection with flora around them. Treants are considered to be similar, except that their magic animates the tree they are formed in. Nymphs are beautiful river spirits. Chwinga are tiny benevolent fairy creatures formed out of a profusion of natural magic. Korred are satyr-ike earth spirits who love to dance and be merry.

Monsters

The Jabberwock is a dragon-like monster thought to be spawned naturally from a large and magical enough forest. The mirage dragon is a dragon (probably green) that has been warped by growing in the feywild and developing natural illusion magic. An obliviax is a kind of sentient moss growth that drains life and memory from its victims, turning them into ambulatory moss-zombies. Many sentient locations, possessive spirits, and other weird creatures also owe their nature to the influence of the fey.