Shade
Monster Junkie
I didn't even consider Aberration. They're unnatural creatures usually, so why would a Woodland Deity create one?
You answered your own question.

Their immunity to sleep, charm, hold, death magic, poisons and cold-based attacks shouted "Undead-like" to me.
Yet they lack the usual "turned as..." that most old-school undead possessed.
Paging Dr. freyar...

Of course Undead are unnatural too, which is one reason I suggested Deathless.
Deathless are unnatural, too.