Illumination is an interesting feature in light (har) of the fact that undying soldiers have 60 feet of darkvision. They’re vulnerable to necrotic damage, resistant to radiant damage and less susceptible to damage from off-the-rack weapons than from ones that are magical or merely silvered. They have ordinary Intelligence and above-average Wisdom, so they’ll talk before fighting and make prudent targeting decisions.
They have very high Strength along with high Constitution and, interestingly, Charisma-although the latter doesn’t seem to power any of their abilities, so we can slot them into the regular brute role. Undying soldiers are mostly elite guards. While other undead are either raised by necromancy, kept from eternal rest by trauma or malevolent entities attempting to cheat death, the undying exist beyond the mortal veil simply because they’re so beloved, the world can’t bear to part with them. The undying of Eberron are a fascinating invention: undead creatures aligned with good.