Actually looking back the problem is mostly with the verb forms:>Thou shall endeth this eternal twilight, and avert further Undead sacrifices.
The correct way to say this would be "thou shalt end">O chosen Undead. Thou hath journey'd far.
Another verb disagreement. Should be "thou hast">thou should assume, and inheriteth the Fire of our world. Thou shall endeth this eternal twilight, and avert further Undead sacrifices.
Should be "thou shouldst" and them "thou shalt end"
I'm pretty sure there are some actual thee/thou confusions, but I can't remember the characters that would have done so.