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.
Does the Trance trait allow an elf to finish a long rest in 4 hours? The intent is no. The Trance trait does let an elf meditate for 4 hours and then feel the way a human does after sleeping for 8 hours, but that isn’t intended to shorten an elf’s long rest. A long rest is a period of relaxation that is at least 8 hours long. It can contain sleep, reading, talking, eating, and other restful activity. Standing watch is even possible during it, but for no more than 2 hours; maintaining heightened vigilance any longer than that isn’t restful. In short, a long rest and sleep aren’t the same thing; you can sleep when you’re not taking a long rest, and you can take a long rest and not sleep.
Here’s what this all means for an elf. An elf can spend 4 hours in a trance during a long rest and then has 4 additional hours of light activity. While an elf’s companions are snoozing, the elf can be awake and engaged in a variety of activities, including carving a lovely trinket, composing a sonnet, reading a tome of ancient lore, attempting to remember something experienced centuries before, and keeping an eye out for danger. The Trance trait is, ultimately, meant to highlight the otherworldly character of elves, not to give them an edge in the game.
That all said, if you’re the DM and you decide to let Trance shorten an elf’s long rest, you’re not going to break the game. You are making a world-building choice if you do so. You’re deciding that elves, on a global scale, are ready to reenter a fight before anyone else, that they heal faster than most humanoids, and that they regain their magical energy faster. Such a choice would make sense in a world where elves are the dominant race, where they not only live longer than others, but also recover faster.
No, Filcat's answer is the current one. That link is from 2015 and no longer holds after being clarified in recent sage advice and errata (and, if I remember correctly, a recent reprinting of the PHB).
An Elf gets all the benefits of a long rest after 4 hours.
Does the Elven trance qualify as a long rest for spell replenishment?
Perpetually annoyed that Eldritch Knights can't use Eldritch Blast, Eldritch Smite, and Eldritch Sight.
Yes. From the Sage Advice:
Short Answer: Yes
and No.from: http://dnd.wizards.com/articles/features/rules-answers-september-2015Edited as per: ratwhowouldbeking
Rule number 1 of the Forums: listen to filcat
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Thanks folks
Perpetually annoyed that Eldritch Knights can't use Eldritch Blast, Eldritch Smite, and Eldritch Sight.