5th Edition
Half Eladrin:
Medium Humanoid Outsider, Fey
+2 Cha
+1 to any 2 other Attributes
Movement: 30
Darkvision: 30ft
Fey Ancestry: Advantage vs charm, immune to magical sleep
Mixed Heritage: can take Background and feats that require Human or Elven or Fey as a Prerequisite
Fey Step: misty step 1/long rest (minor Presdigitation effects, snow flakes, fallen leaves, Flower Petals, Warm Breeze) depending of Eladrin Parent
Seasonal Acclimation: after short rest make Con Save DC: 8+ Weather modifiers:
Success gives Advantage on hourly checks for extreme weather conditions
Or (optional) gain Resistance to Natural Weather effects
Languages Common, Elven, Sylvan
Reduced Darkvision
No keen senses
No Extra skill Proficiencies
No Trance
No Seasonal fey step game mechanic effects
Gives the Flair of the Seasonal subtype, but in a really passive way.
Heh, now that ability score improvements are determined separately while choosing background, it is weird to see the old way of doing things as part of race.
Essentially your Human-Eladrin has:
• Fey
• Darkvision
• Charm Resistance
• Sleep Immunity
• Misty Step (thematic)
• Weather Resistance
Compare the Elf from the UA playtest:
• Humanoid
• Darkvision
• Charm Resistance
• Trance
• Sleep Immunity
• Perception proficiency
• Cantrip
• Level 1 spell at level 3
• Level 2 spell at level 5 (Misty Step)
CREATURE TYPE
Altho the standard Elf is Humanoid, Fey Elf exists in the Monster Manual, and Fey can be a playable character so that is possible. I am fine with the Eladrin being either: Celestial, Humanoid, or Fey (players choice).
It occurs to me, if the character is Fey, then there is no "Fey Ancestry", the character is simply Fey.
DARKVISION
As a DM, I dislike tracking light source radiuses. So, similarly, if the Darkvision is only 30 feet, I would need to keep track of that when describing a scene. It would be a nuisance for me. So I would rather make the Darkvision unlimited range, or at least the standard 60 feet which covers most rooms, and at least beyond one move away.
Then again. I feel the Drow should have Darkvision, the Wood culture (and Sea and Shadar-kai) might have Darkvision, but the High and Eladrin cultures shouldnt have Darkvision. If swapping Darkvision out, it is worth a cantrip.
CHARM RESISTANCE
Altho Elf Charm Resistance is a D&D tradition, in 5e as an aspect of Fey Ancestry, it is really a taste of the Magic Resistance (to spells) that many Fey have. Note the Fey Eladrin have full Magic Resistance. Charm Resistance is less powerful but the flavor works ok.
SLEEP IMMUNITY
The Sleep Immunity is actually because of Trance, because the Elf never sleeps. So if having Sleep Immunity, it makes more sense to have Trance too. Since neither the Sleep Immunity nor Trance are powerful, it is fine to include both for the sake of the iconic flavor.
MISTY STEP
The Eladrin in Mordenkainens − and especially the Astral Elf in Spelljammer − is powerful. With Misty Step doable proficiency times per long rest. However the UA walks this back, and instead makes it only a level 2 spell once per day, and only becomes possible when the character reaches level 5. I prefer the Astral Elf design space and feel all races should have a powerful flavorful feature at level 1. So I am still processing how I feel about the UA walk-back. For now I am going with the UA Misty Spell once per long rest at level 5.
Tashas clarifies, a player can reflavor any spell. So it is ok to reimagine what the Misty Step spell looks like when the Eladrin character does it.
If giving up both Darkvision and Perception proficiency, it might be enough design space to upgrade the restricted Misty Step, to a Short or Long Rest at level 1. So this would be the normal "Fey Step". This makes all of the power available at level 1, so it is a big deal. But it looks balanced to me.
WEATHER IMMUNITY / LEVEL 1 SPELL
Note the UA Elf gains a level 1 spell when reaching level 3. It looks safe to swap the spell for Weather Resistance instead. The Weather Resistance is a nonpowerful "ribbon", but has appropriate flavor. I can imagine an Eladrin walking across an arctic glacier in bare feet without any problem, with light aristocratic clothing that is jarringly unsuitable for the harsh weather.
I would characterize the feature as Weather Immunity. Specifically, the Eladrin is immune to nonmagical fire and cold damage, and ignores extreme weather conditions.
The Eladrin would still be vulnerable to magical fire and cold from spells and so on, sot the Weather Immunity is mostly a "ribbon" ability, which can be narratively interesting but rarely matters mechanically in most situations.
CANTRIP
If going with the UA Elf design space, there is still a choice of cantrip left over. It is even ok to swap the cantrip after each Long Rest. So the Eladrin can use the current cantrip to represent a particular season.
For the Eladrin, maybe make the default cantrip be Druidcraft, since it is more in tune with the season weather patterns, and some harmless plant effects as well.
IN SUM
Half Eladrin
• Fey
• Charm Resistance
• Trance
• Sleep Immunity
• Weather Immunity
• Druidcraft (or swap cantrip per long rest)
• Misty Step (per short or long rest)
Remember every character can put a +2 and +1 to any ability scores. So you can choose to put the +2 on Charisma score, then use the +1 for any other score.