The Crystal Eye
The death of the Keeper marked the fall of the corrupted forest. Bit by bit the remaining horrors were hunted down until there was near to none left. And it all happened thanks to the hero party's renewed strengths.
Being able to control darkness like a semi-solid extension of his body–Raven's skills were buffed tenfold. Aria was the same with her now being able to control more clones and charge more powers into her blows. Mel's control of woodland magic was no longer limited to trees, vines, and other vegetation, but she could also summon bugs, vipers, and plenty of carnivores.
As for Amedith, his holy magic and defense were growing surprisingly quickly. Pillars of light to defend a nearby ally, ethereal wings made of pure magic that gave him a much-needed boost in agility, not to mention an even higher resistance to status effects and attacks that may try to debuff him.