If you have 4 Zill Sigils would you add +8d6 sneak attack? If so this race is a brokengood rogue.
And being BleyBleyBleyBley (which means fortunate fortunate fortunate fortunate but we can hope illumian language repeating the same word makes it mean more), you would have +8 to saving throws.
Also look at this:
Shelaesh: Illumians who possess both the shel and aesh sigils have a gift for companionship with animals and magical beasts. Illumians add the number of sigils they have to their character level to determine the capabilities of their animal companion.
Hello, supermount class, meet Illumian. Let's have tea.
And this is even better:
Uurkrau: Illumians possessing both the uur and krau sigils have their arcane spell failure chance reduced by 10% for each sigil they possess. Many illumians with both uur and krau are fighter/wizards.
Yes, Uur and Krau sigils are crap independently but stick them together and they apparently spell the Illumian word for awesome, since you are going to possess 6 sigils at level 20 you are basically ignoring any spell failure of 60% and less. Hello full plate caster.
If LA buy-off and this race is allowed, Take it! It is crazy brokengood. 6 Zill sigils is +18d6 sneak attack, and you could stick that on a full caster build if you wanted to. 6 Bley sigils is +18 to all saving throws, which is perhaps the best thing you can get from this.
I would so want to make an UurKrauBleyBleyBleyBley Illumian Gish with these rules. Look at me, I'm running around with +12 to all saves and full plate and I'm a full caster. Whatcha gonna do about it?