Source: Player's Handbook

• Ability Score Increase. Your Charisma score increases by 2, and two other ability scores of your choice each increase by 1.

• Age. Half-elves age at much the same rate as humans, reaching adulthood at the age of 20. They live much longer than humans, however, often exceeding 180 years.

• Size. Half-elves are more or less the same size as humans, ranging from 5 to 6 feet tall. Your size is Medium.

• Speed. Your base walking speed is 30 feet.

• Darkvision. Thanks to your elven heritage, you have superior vision in dark and dim conditions. 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 can't discern color in darkness, only shades of gray.

• Fey Ancestry. You have advantage on saving throws against being charmed, and magic can't put you to sleep.

• Skill Versatility. You gain proficiency in two skills of your choice.

• Languages. You can read, speak, and write Common, Elven, and one language of your choice.

Source: Sword Coast Adventurer's Guide

• Some half-elves in Faerun have a racial trait in place of the Skill Versatility trait. If your DM allows it, your half-elf character can forgo Skill Versatility and instead take the elf trait Keen Senses or one of the following traits based on your elf parentage:
  • Elf Weapon Training (High or Wood Elf Heritage). You have proficiency with the longsword, shortsword, shortbow, and longbow.
  • Cantrip (High Elf Heritage). You know one cantrip of your choice from the wizard spell list. Intelligence is your spellcasting ability for it.
  • Fleet of Foot (Wood Elf Heritage). Your base walking speed increases to 35 feet.
  • Mask of the Wild (Wood Elf Heritage). You can attempt to hide even when you are only lightly obscured by foliage, heavy rain, falling snow, mist, and other natural phenomena.
  • Drow Magic (Dark Elf Heritage). You know the Dancing Lights cantrip. When you reach 3rd level, you can cast Faerie Fire once, and it recharges after a long rest. When you reach 5th level, you can cast Darkness once, and it recharges after a long rest. Charisma is your spellcasting ability for these spells.
  • Swim Speed (Sea Elf Heritage). You have a swimming speed of 30 feet.

Source: Eberron - Rising from the Last War

If your Half-Elf has the Mark of Detection, these features replace the Ability Score Increase and the Half-Elf Versatility traits.

• Ability Score Increase. Your Wisdom score increases by 2, and one other Ability Score of your choice increases by 1.

• Deductive Intuition. Whenever you make a Intelligence (Investigation) or a Wisdom (Insight) check, you can roll a d4 and add the number rolled to the total ability check.

• Magical Detection. You can cast the Detect Magic and the Detect Poison and Disease spells with this trait. Starting at 3rd level, you can also cast the See Invisibility spell with it. Once you cast either spell with this trait, you can't cast that spell again until you finish a Long Rest. Intelligence is your Spellcasting Ability for these spells, and you don't require material components for them.

• Spells of the Mark. If you have the Spellcasting or Pact Magic class feature, the spells on the Mark of Detection Spells table are added to the spell list of your Spellcasting class.

Mark of Detection Spells

Source: Eberron - Rising from the Last War

If your Half-Elf has the Mark of Storm, these features replace the Ability Score Increase and the Half-Elf Versatility traits.

• Ability Score Increase. Your Charisma score increases by 2, and your Dexterity score increases by 1.

• Windwright's Intuition. Whenever you make a Dexterity (Acrobatics) check or any Ability Check involving Navigator's Tools, you can roll a d4 and add the number rolled to the total ability check.

• Storm's Boon. You have resistance to Lightning damage.

• Headwinds. You know the Gust cantrip. Starting at 3rd level, you can also cast the Gust of Wind spell with it. Once you cast this spell with this trait, you can't cast that spell again until you finish a Long Rest. Charisma is your Spellcasting Ability for this spell.

• Spells of the Mark. If you have the Spellcasting or Pact Magic class feature, the spells on the Mark of Storm Spells table are added to the spell list of your Spellcasting class.

Mark of Storm Spells