Shadow tattoos that are shadowflux images living in the skin. Really painful to pull out and use as a weapon but possible.
Shades have the ability to create corporeal shadows AND transfer sounds through them: Shades that produce shadow instruments to play music during parties.
Shades actually prefer nightlights compared to other elves. It levels the area to a more even light/dark ratio that they can work with--and live with--easier than an overwhelming shadowy presence. Similar to how you should never leave a hydrokinetic unchecked in Atlantis.
Tam and Linh to me kinda have that moon dynamic, obviously. Linh is the bright side of the moon that you see, that has a push and pull with the ocean, is the comforting presence in the night. Tam is the dark side of the moon (Mulancore), always there, unnoticed, mysterious, still supportive.
Elemental abilities have the highest rate of multiple births, subelementals (charger, froster, psionipath, etc) coming in second. Maybe gives another layer to the elven prejudice against twins/multiple births AND elemental abilities. Because elements are so intertwined, they are actually more powerful in sets. As I said with Tam and Linh, two sides of the same coin. One side is not as strong without the other. Multiple births are frowned upom because the elves in power were scared of unchecked power, not because they were scared of a lack of it. (Always a balance between general greatness and controllable that any ruler wants in their population).
I know another one I saw, which may be canon, but vanishers and shades are able to see each other when others can't. And that is because the light and shadow manipulation cancel each other. (My Tiana heart).
Elementals are also the least likely to come with a second ability. They take up a lot of energy, and so elves of this nature have weaker technopathic or polyglot genes than the average elf (those being such base level, common abilities that almost every elf has them in some capacity; another headcanon that isn't quite mine but fits well here)
Alternatively to what I just wrote, because this one IS actually mine, but technopathy is the elven ability of earth. It isn't technology, it has nothing to do with math equations or formulas, it is simply the understanding and manipulation of the earth. How to bend it to your will, but because the earth is the most grounded element it requires more complexity and more physicality to manipulate than a volatile one like fire (that is very emotions based and can be quite unruly).
Just as a vanisher is basically a flasher lite, a phaser is a technopath lite. Or, earth element lite.
If you really want someone that is PEAK technology, a charger and a technopath duo would create something awesome (wait, I have OC best friends of these abilities--)
Flashers create similarly physical light creations that you can interact with. I'm remembering Unlocked when they crossed that rainbow bridge to get to the Neverseen hideout...I want more of that. RAINBOW ROADS PEOPLE.
Elemental elves have each the ability to provide a purified, or most powerful, form of their element. For celestial elements (fire, shadow, and light) it is the obvious everblaze, quintessence, and shadowflux. For terrestrial elements (earth, water, air) it is less destructive and more beneficial. Hydrokinetics are in charge of producing the fountain of youth water. Powerful hydrokinetics can purify water to its most perfect state and that's what they do. I haven't decided how gusters and I guess technopaths are included in this.
Someone in the comments mentioned shades gradually seeing more and more lights, until maybe their vision is just white and everything is reflecting off of their eyes. I raise you flashers who are all synesthetics. In fact, it is almost impossible in their demographic to have a flasher that isn't. Wylie and Rayni would fight over Tam and Linh's auras and poor them (and Tiergan) would have to hear it. It is kinda like when Team Valiant entered that dark room and the auras of their abilities surrounded them, but more complex and not always in agreement.
Flashers CAN suck light from a room. Or, rather, they can remove color. They can manipulate what colors people see (all or none). Which kind of crosses over into shade category but shades also deal in physical shadows, which flashers cannot do.
Telepaths are obviously the most respected ability and I think the council has a host of them mind printing their public announcements onto a bunch of scrolls, which conjurers send out en masse. Less writing, but it takes a very strong telepath and the stronger the more one can "print" at one time.
P.S. I want to hear more of yours for shades PLEASE