Sea Elf

Creature Type. You are a Humanoid. You are also considered an elf for any prerequisite or effect that requires you to be an elf.

Speed. Your walking speed is 30 feet, and you have a swimming speed equal to your walking speed.

Child of the Sea. You can breathe air and water, and you have resistance to cold damage.

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.

Friend of the Sea. Aquatic animals have an extraordinary affinity with your people. You can communicate simple ideas to any Beast that has a swimming speed. It can understand your words, though you have no special ability to understand it in return.

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 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 one other language that you and your DM agree is appropriate for your character.

Elves of Many Realms

Created by the god Corellon, the first elves were Fey beings who cavorted on various planes of existence, changing their physical forms at will. Outside the glory of Arvandor, their favourite place was the feywild—a realm of unbridled passion. It was to that place of splendors that elves fled after they were exiled from Corellon's presence for plotting with their god's rival, Lolth. And it was there that they transformed from Fey creatures into Humanoids and lost their ability to shape-shift at will. Afterward, they often wept as they realized what they had lost, their sorrow made even deeper by the Feywild's influence. But in the Feywild, they also discovered the potential joys of being people of fixed forms, and they rediscovered hope once they renounced Lolth's treachery.

Most elves eventually spread from the Feywild to other worlds, as wanderlust and curiosity drove them to the far reaches of the multiverse. In those other worlds, elves developed the physical forms now associated with them. Because of their original mutable nature, each group of elves mystically took on characteristics of the environment with which they bonded, whether forests (wood elves), fey crossings in the Material Plane (high elves), the Underdark (drow), the Shadowfell (shadar-kai), the Feywild (eladrin), or oceans (sea elves).

In some places, Corellon has passed from elves' memory, but the god's blood flows within them still, even if they know nothing of its source. That blood is what causes them to evolve after spending centuries connected to a particular environment, so it is only a matter of time before other kinds of elves emerge.