Elves are the classic race choice in fantasy RPGs. Everyone has an elf, and every game needs an elf. What is an elf? Usually magic, probably all around better than you, always has pointy ears, that sort of thing. In a bit of meta commentary though, now-a-days, what makes elves stand out is the plethora of different elves. Find a campaign setting, splat book, or homebrewer, who doesn’t write up their own elven variants. 5e literally has 37, if I include half-elven options. Heck, they have 3 different types of Wood Elves, (1 in the PHB, and 2 in Wayfarer’s Guide). There are a lot of elves. So, I’m going to do the sensible thing and write my own take. This take brings something new to the table (and I and others have been muttering about something to this effect for years), while still allowing you to play your Mul Dayan elves if you insist. It lets you play RAW elves, but still mix it up, and gives a reason for there to be 37 variants of the same thing. Even if you love elves, how many elven PCs are you really making? 37?
So what are elves?
Elves are a long-lived race. So long, I doubt the PHB limit of 750 years is firm, and some elves probably stopped tracking preferring to guess, measure age in decades (only celebrating on the decade), or simply went past that with 750 being the average.
Elves are vaguely magical. All elves have some arcane powers. Usually something with a cantrip or minor spell inherently, but other times its proficiency in arcana, or a vaguely fey-themed magic power.
Elves are fey adjacent. Elves aren’t fey, but they probably tie in somewhere. No one bats an eye at the elf in the fey court, even if the elf isn’t always fey. It’s a thing.
We need to keep these three things and make them the focal point of elves. My answer has some vaguely nature themed magic, and ties into their long lifespans.
So how do we make them different?
Elves adapt. They don’t have a billion subraces. In reality, there is one type of elves. Elves. That said, elves are like Eevees. They are a type of minor fey adjacent creature, whose main trait is their connection to the natural world. An elf is always in tune with nature. So in tune, that they begin to take on traits of the landscape in which they reside. Wood elves live in forests, and their hair is the color of autumn leaves, and their skin may even start to get mossy or bark-like. Sea elves live on the shore. After enough time, they developed a swim speed and the ability to breathe underwater. Drow? They were banished underground and adapted. High elves? Well, they’ve spent their entire lives studying arcane magic in wizard towers. Now they are extra magic infused. Astral elves? Elves who have lived in the astral sea. Shadra-kai? The Shadowfell. Avriel? Elves who lived their lives in rocky outcroppings and grew wings.
So what do we do?
This is another easy house rule for you. Go ahead and say that an elven PC who spends a year in a given terrain is able to adjust their subrace to one that is appropriate. A year is enough time for your munchkin players not to do it every session, but it could come up between adventures during a campaign, or at least be plausible for an NPC to do. A wood elf who takes up piracy, and spends all their time on the high seas finds their barky skin shift into a sharkskin texture, and some gills grow in. If they get lost in the underdark for an extended duration, they can eventually just see in the dark. Move to the plane of fire? They pick up fire resistance.