Soo-Won is corrupted at Dragon's End

Soo-Won, the Elder Dragon of Water and Life, is revealed in End of Dragons’ finale to be the original "One Elder Dragon": the mother of the other Elder Dragons, who once balanced all of Tyria's magic alone. To keep the world stable she had sustained herself in seclusion, but when her containment is sabotaged at Dragon's End her mind begins to fall to Void magic, threatening a catastrophe should she die with that corruption unextracted.

Her corruption forces the final confrontation of the era, in which Glint's scion Aurene (already the Elder Dragon of Crystal and Light) is set to inherit the duty of filtering the world's magic once the last of the old cycle's dragons is gone.