Elves in the Known World are greatly varied, being from two different origins. The Southern elves
emigrated from Evergrun before the Great Rain of Fire. The shadow elves traveled underground to escape the disaster and settled in large caverns underneath the continent. Another group of elves, the Belcadiz came from another land far over the ocean. They are further broken down by where they settled.
There are no Drow in Mystara, sylvan and high elves have different names in Mystara.
All Elves in Mystara lose the Trance ability.

Sylvan Elves
Located in Alfheim, Glantri and Karameikos mainly, Sylvan elves are by far the most numerous. Sylvan elf males tend to grow long white beards late in life. As a Sylvan elf, you have keen senses and intuition, and your fleet feet carry you quickly and stealthily through your native forests. Sylvan elves’ skin tends to be copperish in hue, sometimes with traces of green. Their hair tends toward browns and blacks, but it is occasionally blond or copper-colored. Their eyes are green, brown, or hazel.
Ability Score Increase. Your Wisdom score increases by 1.
Elf Weapon Training. You have proficiency with the longsword, shortsword, shortbow, and longbow.
Fleet of Foot. Your base walking speed increases to 35 feet.
Mask of the Wild. You can attempt to hide even when you are only lightly obscured by foliage, heavy rain,
falling snow, mist, and other natural phenomena.
Belcadiz Elves
Located exclusively in Glantri, Belcadiz are known for their fiery passions and extravagant
clothing. Their men are noted for sporting short thin beards. Belcadiz elves are shorter
than normal elves, and possess darker skin and almost always black hair, though brown and
rarely red hair can be found. As a belcadiz elf, you have a keen mind and a mastery of at least the basics of magic.
Ability Score Increase. Your Intelligence score increases by 1.
Elf Weapon Training. You have proficiency with the rapier, shortsword, shortbow, and longbow.
Cantrip. You know one cantrip of your choice from the wizard spell list. Intelligence is your spellcasting ability for it.
Extra Language. You can speak, read, and write one extra language of your choice.
Shadow Elves
As a shadow elf you have lived your life underground waiting for the return of your people to the surface. Your people were split off from the rest of your race in the Great Rain of Fire and have spent thousands of years underground not knowing what was left of the surface world. You come from a deeply religious people who are just now discovering there are entire civilizations above you.
Shadow elves are known for their pale skin and light hair. Their ears are larger than other elves, it is a giveaway in the company of others of their type.
Ability Score Increase: Your Wisdom score is increased by 1.
Bonus Proficiency: You are proficient in the Religion skill.
Elf Weapon Training: You have proficiency with the long sword, short sword, crossbow and spear.
Superior Dark Vision: You can see in dark or twilight conditions up to ninety feet as if they were bright daylight.
Sea Elves
The sea elves are a tribe of elves native to the Minrothad Guilds. They are known for their uncanny sense of direction, ingrained from years at sea. They are an adventurous people, spending more of their time at sea than on land. There is some minor distrust among sylvan elves for a resemblance to shadow elves, but the similarity is purely coincidental.
Ability Score Increase: Your Intelligence score raises by 1.
Elf Weapon Training: You have proficiency with the long sword, rapier, long bow and trident.
Bonus Tool Proficiency: You are proficient with vehicles (water).
Sense of Direction: You gain advantage on all Wisdom (Survival) tests you make for navigation.
Vyalia Elves
Located in Thyatis and Karameikos, the reclusive Vyalia are expert foresters, known for their ability to disappear into the forest without a trace. While they keep to themselves mostly, the Empire of Thyatis has contracted them on multiple occasions to teach the way of the eldritch knight to human soldiers. The Vyalia otherwise stay by themselves, and are remote enough that the countries they live in leave them alone.
Ability Score Increase: Your Intelligence score raises by 1.
Bonus Proficiency. You have proficiency with the Nature skill.
Hidden Trails: You can cast pass without trace once using this trait. You regain the ability to do so after a short rest.