What does an Aquatic Half-Elf Variant mean?

Question

Though I know this has been addressed somewhat here, here, and here, I am still getting a little confused on what changes come to half-elf variants when it comes to looks, ability differences, and heritage.

I understand that the main source of confusion comes from DnDBeyond, where their search lists Half-Elves as either Drow Half-Elf, Aquatic Half-Elf, High Half-Elf, Wood Half-Elf, Mark of Detection Half-Elf, or Mark of Storm Half-Elf, though all links draw back to this description:

Some half-elves in Faerûn 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 a trait-based on your elf parentage:

Which is, itself a reference to the Sword Coast Adventurer's Guide (p. 116):

HALF-ELF VARIANTS
Some half-elves in Faerûn 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 a trait based on your elf parentage:

• A half-elf of wood elf descent can choose the wood elf's Elf Weapon Training, Fleet of Foot, or Mask of the Wild.
• A half-elf of moon elf or sun elf descent can choose the high elf's Elf Weapon Training or Cantrip.
• A half-elf of drow descent can choose the drow's Drow Magic.
• A half-elf of aquatic heritage can choose a swimming speed of 30 feet.

But, for me, that rose even more questions on what physical traits the variants would have as even the SCAG (P. 106) only offer vague footnotes on the Elvish parents such as "Sea elves live in the sea!" (and even more kinds of elves)

So in hopes to find another official source that would describe these variants in more details, I found Unearthed Arcana (2004) (Thinking it was an Unearthed Arcana for 5e) that did bring up the Sea version of every race, giving additional variation to the Aquatic Half-Elf, such as dim vision, a "Bonus Language" that allowed them to learn a secret language, and a possible Amphibian Trait to breathe both on land and in the water. However, in that case, it stated Aquatic Half-Elves were the children of Sea Elves and Sea Humans. I have avoided Fandom sites as I am unsure which ones are official and which are just homebrew, though I guess I still followed the wrong source.

Edit Notes:

An additional fact is Half-Elves have 2 sections in the PHB (Of Two Worlds and Diplomat or Wanderer) that suggests they can visit either parent, and their eyes favor the Elf. Which would mean that Drow Half-Elves, for example, would have pale near-white eyes and be able to travel into the Underdark. But wouldn't that mean that Aquatic Half- Elves have whatever type of eyes Sea-Elves do and be able to live under the sea?

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Putting this all together, I would like to know more information on Half-Elf Variants, specifically the Aquatic Half-Elf and hopefully be directed in more official sources:

Looks:

• What do Sea Elves look like? (Skin colour, eye colour, hair, gills?)
• Do Aquatic Half-Elves take more physical attributes from their Elvish heritage than the eyes? (Similarly, do Drow Half-Elves have Ashen skin?)

Attributes:

• Do Aquatic Half-Elves have an amphibian trait, or are they the only Half-Elf who cannot live with either parent?
• If you forgo the Skill Versatility for a Half-Elf Variant, does that affect their ability to gain racial feats such as Prodigy (XGtE, p. 75)?

Answer 1

"Aquatic Elves" are Sea Elves; therefore, "Aquatic Half-Elves" are half-Sea Elves

The half-elf variant was first published in the Sword Coast Adventurer's Guide (SCAG), which was released in 3 November 2015 (according to Google). Back then, they had not released an official Sea Elf subrace for 5e, so this wording of "aquatic elf" was probably to allude to their existence (since Sea Elves did exist in previous editions and were therefore established in the Forgotten Realms lore, etc) without explicitly stating Sea Elf (because then people might be like "What Sea Elf? There's no Sea Elf subrace (in 5e)?"). At least, that's my guess.

Then, in Mordenkainen's Tome of Foes (MToF), which was released in 29 May 2018, the official Sea Elf subrace was released (after their trial in UA a few months beforehand). Now there is actually an official subrace, this "aquatic elf" reference resolves to the Sea Elf. In other words, had they first published the half-elf variant rules either in or after MToF, they would have likely just said "sea elf", but because SCAG was released beforehand, they went with "aquatic elf" instead.

As far as I'm aware, 5e makes no mention of "aquatic humans", this must have been something only in that "Unearthed Arcana" that you found, which wasn't 5e Unearthed Arcana. At the very least, it's not a thing in official 5e. Half-Sea Elves would simply be the product of Humans and Sea Elves. To be honest, D&DBeyond probably ought to just rename the "Aquatic Half-Elf" entry to Half-Sea Elf instead, since Sea Elves have now been released.

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• What do Sea Elves look like? (Skin colour, eye colour, hair, gills?)

SCAG (p. 106) and MToF (p. 62) give us very brief descriptions of them, but unfortunately what they look like is not mentioned. There is a picture of them in MToF (p. 63), from which we can infer that they have blue skin and webbed hands and feet, but little else. It might be worth looking to previous editions of D&D to find out more about sea elves, unfortunately.

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• Do Aquatic Half-Elves take more physical attributes from their Elvish heritage than the eyes? (Similarly, do Drow Half-Elves have Ashen skin?)

SCAG doesn't tell us much about their appearance, but the PHB does give us this hint on page 38:

Half-elven coloration and features lie somewhere between their human and elf parents, and thus show a variety even more pronounced than that found among either race. They tend to have the eyes of their elven parents.

So yes, eyes are mentioned explicitly, but that note on coloration and features imply that Half-Drow would have ashen skin (though not as dark as a Drow) and Half-Sea Elves would have blue skin (though probably an off-blue, not as strong as a Sea Elf), and would likely have webbed hands and feet (although perhaps only slightly webbed), but the details are left intentionally vague as so not to impose "rules" about appearance on any player creating a half-elf character, since 5e in particular empowers the player to define their character (see also where most notes on alignment use terms like "tend to" as so not to pigeon-hole PCs into specific alignments either).

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• Do Aquatic Half-Elves have an amphibian trait, or are they the only Half-Elf who cannot live with either parent?

That part of SCAG you quoted only includes a swim speed, not the ability to breathe underwater, so it would appear that a Half-Sea Elf would not be able to live in the sea with their elven parent (unless they have magic items that allow them to breathe, but that's a tangent I'm not exploring), but there's nothing to say that a Half-Sea Elf couldn't live with their human parent.

That said, you raise a good point (in a comment): "The others seem to have full traits like Fleet of Foot when Sea Half-Elf is so close to be Child of the Sea (MToF)"; now that MToF has released the official Sea Elf subrace, the variant option for an "aquatic half-elf" in SCAG does seem rather lackluster now.

I'd guess that if they were releasing variant Half-Elves alongside or after MToF, they'd have possibly written that Skill Versatility can be swapped out for Child of the Sea rather than just a swim speed by itself, and this would better match the other Half-Elf variant options who get an actual named trait from their elven counterparts.

I'd say that a DM would be well advised to houserule that an "Aqautic Half-Elf" (i.e. Half-Sea Elf) using the Variant Half-Elf rules should get the full "Child of the Sea" trait from the Sea Elf subrace, rather than just a swim speed. This also makes more sense lore-wise, since then a Half-Sea Elf can live alongside their elven parents, rather than being "excluded", as you pointed out.

Also, just a swim speed? Anyone can learn how to swim, right (narratively, I mean; I know that, mechanically, gaining a swim speed is not as simple)? Narratively, it doesn't really feel like your Sea Elf heritage is manifesting particularly strongly, and mechanically, it seems like a weak trade for Skill Versatility...

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• If you forgo the Skill Versatility for a Half-Elf Variant, does that affect their ability to gain racial feats such as Prodigy (XGtE, p. 75)?

A Half-Elf is a Half-Elf, regardless of what racial features they have. If they are a Half-Elf, they have access to the Prodigy feat. Being a variant Half-Elf does not affect this.