DISCLAIMER:I want to use only ACTUAL rules in SR4A, Street Magic, Digital Grimoire, and Runner's Companion.
Ideas that start with suggesting house rules should go in the trash, where house rules belong in and of themselves.

Now, that said...I have been familiar with Earthdawn for a while, and while most of the spellcasting types
are rather easy to figure out, I have found that the Nethermancer is the most difficult to pin down exactly
how one would make such a character. So, i figured I would ask on here: If you were to build an
Awakened character based of the Nethermancer concept, how would you do it? What traits, spells,
skills, etc would you give that starting character?

Well just for quick reference, could you tell what they were able to do in ED?
I red the rules some time ago but cant remember what they actually did.
I vaguelly remember them doing stuff with spirits and generally subtle magic. But nothing specific.

they were creepy....
so very creepy...

specifically they would simply be another magical tradition, I personally would pick voodoo as the base for mechanics.

They studied life, death, spirits, and the planes. They specialized in being creepy, frightening people off from Things Namegivers Were Not Meant To Know, and trying to find ways to detect and defeat the Horrors.

Grabbing my copy of ED1, these were their signature Spells:

Bone Dance (allowed you to put someone in a controlled seizure to take them out of combat)
Command Nightflyer (communing with bats and other nocturnal aeronauts)
Dry and Wet (@set dampness={0,1})
Experience Death ('nuff said)
Ethereal/Friendly Darkness (impenetrable magical darkness that all Nethermancers/friends can see through)
Nethermark (creates a permanent spell targeting link)
Pain (immobilizes target with crippling pain)
Pass Ward (supreme magical protection with a password)
Pocket Guardian (summons a spirit that bites anyone who picks your pocket)
Recovery (boots natural healing by ~1/4)

Bone Dance: Some variation of Controll Actions?
Command Nightflyer: Restricted target Mindlink.
Dry and Wet: Enviromental manipulation of some kind. Shape [Water] ?
Experience Death: Maybe could be singletarget Foreboding turned up to eleven.
Ethereal/Friendly Darkness: Difficult, especially the friendly see through part. Use spirit with concealment?
Nethermark: No idea.
Pass Ward: Ward with a twist?
Pocket Guardian: Low force spirit + Long Term Binding( or whatever the name was)
Recovery: Increasing body increases natural healing.

Just quick ideas.

Spell match is for mechanics
description/effect of the spells change to match as needed.

Bone Dance: Bugs,
Command Nightflyer: Translate
Dry and wet: custom spell varient of "shape [element]" or "Alter Temperature"
Experience Death: Agony
Ethereal/Friendly Darkness: Shadow
Nethermark: requires ritual magic
Pass ward: Ritual magic again
Pocket Guardian: summon watcher
Recovery: Heal

My ED books are in the attic, so I can't look up the spells, but you need some higher circle spells too imo. ED circle 1-2 spells are a lot weaker than SR magic - ED magic is balanced around swords and arrows, SR magic around assault rifles, cyberware and drones.

I think you just need to take their spells and find something existing that works like it. For Bone Dance being Bugs is right on.

Didn't they have skin shift? That could be death touch or manabolt (can't remember if it it was touch or ranged).

Iirc there was some death mask spell that scared people trying to attack you? You could have that as an illusion spell that worked much like combat sense, making it harder for people to attack you.

I wouldn't go with a possession based tradition, instead have some of the spirits look at and act like the summoning spells nethermancers have, they were very nethermancer defining imo.

That would be nice to see that concept done I could have a cast of npcs made around it.

Agony is an interesting interpretation, but what I meant was "Experience the final moments of a dead Namegiver's life [to find out how they died]".