Eladrin were born out of the conflict between Wild Fey and Shadow Fey, and of all the elven races, their nature is perhaps most strongly determined by Feywild and Shadowfell influences. Like Changelings, they are capable of shifting their natures to embody different aspects of the Shadow-Wild and its conflict. Eladrin can embody four unique natures, each of which is conflated to a season on The Material Plane.

Autumn is the season of peace and goodwill, when summer’s harvest is shared with all. This phase embodies the aspects of the Feywild and the Shadowfell which share a desire for peace and community.

Winter is the season of contemplation and dolor, when the vibrant energy of the world slumbers. This phase embodies the muted, contemplative aspects of The Shadowfell.

Spring is the season of cheerfulness and celebration, marked by merriment as winter’s sorrow passes. This phase embodies the whimsical, carefree aspects of The Feywild.

Summer is the season of boldness and aggression, a time of unfettered energy. This phase embodies the aspects of hostility and violence shared by The Feywild and The Shadowfell.

Some eladrin remain associated with a particular season for their entire lives, whereas other eladrin transform, adopting characteristics of a new season. When finishing a long rest, any eladrin can change their season. An eladrin might choose the season that is present in the world or perhaps the season that most closely matches the eladrin’s current emotional state. For example, an eladrin might shift to autumn if filled with contentment, another eladrin could change to winter if plunged into sorrow, still another might be bursting with joy and become an eladrin of spring, and fury might cause an eladrin to change to summer.

Relations of other Races
Description

Physical Appearance
While eladrin have a typical elven frame with long pointed ears and slender features, their coloration changes with their chosen season, shifting to match the colors they associate with their season.

Ability Score Increase
Increase one score by 2 and increase a different score by 1, or increase three different scores by 1. You can't raise any of your scores above 20.

Creature Type
You are a Humanoid, with the secondary creature type of Fey. Wheter you are Wild Fey or Shadow Fey depends upon your current season. You are Humanoid-[Fey] (Elf, Eladrin)

Age
Although elves reach physical maturity at about the same age as humans, the elven understanding of adulthood goes beyond physical growth to encompass worldly experience. An elf typically claims adulthood and an adult name around the age of 100 and can live to be 750 years old.

Size
You are Medium.

Speed
Your walking speed is 30 feet.

Darkvision
You can see in dim light within 60 feet of you as if it were bright light and in darkness as if it were dim light. You discern colors in that darkness only as shades of gray.

Fey Ancestry
You have advantage on saving throws you make to avoid or end the charmed condition on yourself.

Fey Step
As a bonus action, you can magically teleport up to 30 feet to an unoccupied space you can see. You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

When you reach 3rd level, your Fey Step gains an additional effect based on your season; if the effect requires a saving throw, the DC equals 8 + your proficiency bonus + your Intelligence, Wisdom, or Charisma modifier (choose when you select this race):

Autumn (Either). Immediately after you use your Fey Step, up to two creatures of your choice that you can see within 10 feet of you must succeed on a Wisdom saving throw or be charmed by you for 1 minute, or until you or your companions deal any damage to the creatures.

Winter (Shadow Fey). When you use your Fey Step, one creature of your choice that you can see within 5 feet of you before you teleport must succeed on a Wisdom saving throw or be frightened of you until the end of your next turn.

Spring (Wild Fey). When you use your Fey Step, you can touch one willing creature within 5 feet of you. That creature then teleports instead of you, appearing in an unoccupied space of your choice that you can see within 30 feet of you.

Summer (Either). Immediately after you use your Fey Step, each creature of your choice that you can see within 5 feet of you takes fire damage equal to your proficiency bonus.

Keen Senses
You have proficiency in the Perception skill.

Trance
You don’t need to sleep, and magic can’t put you to sleep. You can finish a long rest in 4 hours if you spend those hours in a trancelike meditation, during which you retain consciousness.

Whenever you finish this trance, you can change your season, and you can gain two proficiencies that you don’t have, each one with a weapon or a tool of your choice selected from the Player's Handbook. You mystically acquire these proficiencies by drawing them from shared elven memory, and you retain them until you finish your next long rest.

Languages
You can speak, read, and write Common and Elvish. Elvish is fluid, with subtle intonations and intricate grammar. Elven literature is rich and varied, and their songs and poems are famous among other races. Many bards learn their language so they can add Elvish ballads to their repertoires.