Sage Advice : Racial Traits
Does the Trance trait allow an elf to finish a long rest in 4 hours?
If an elf meditates during a long rest (as described in the Trance trait), the elf finishes the rest after only 4 hours. A meditating elf otherwise follows all the rules for a long rest; only the duration is changed.
[This answer has been altered as a result of a tweak to the rules for a long rest, which appears in newer printings of the Player’s Handbook.]
Do the lightfoot halfling and wood elf hiding racial traits allow them to hide while observed?
The lightfoot halfling and wood elf traits—Naturally Stealthy and Mask of the Wild—do allow members of those subraces to try to hide in their special circumstances even when observers are nearby. Normally, you can’t hide from someone if you’re in full view. A lightfoot halfling, though, can try to vanish behind a creature that is at least one size larger, and a wood elf can try to hide simply by being in heavy rain, mist, falling snow, foliage, or similar natural phenomena. It’s as if nature itself cloaks a wood elf from prying eyes—even eyes staring right at the elf! Both subraces are capable of hiding in situations when most other creatures can’t, but neither subrace’s hiding attempt is assured of success; a Dexterity (Stealth) check is required as normal, and an observant foe might later spot a hidden halfling or elf: "I see you behind that guard, you tricksy halfling!"
Can a dragonborn sorcerer with a draconic bloodline have two different kinds of Draconic Ancestry?
A dragonborn sorcerer can choose a different ancestor for the racial trait and for the Dragon Ancestor feature. Your choice for the racial trait is your actual ancestor, while the choice for the class feature could be your ancestor figuratively—the type of dragon that bestowed magic upon you or your family or the kind of draconic artifact or location that filled you with magical energy
Written by Jeremy Crawford (Sage Advice Compendium v2.3)