@Salient Love the idea of Broken!Shreya
If I had to do Broken!Horned One, I think I would focus inverting the Horned One’s instincts and animal affinity.
Horror themes: body transformation into different animal parts, dark predators, animals spies and always feeling watched, men consumed by primal and bestial instincts, the terror of always being vulnerable to an ambush or surprise attack. Unremitting howling, punctuated by unnatural silence.
Bonegnasher (Gnasher for short) themselves (the Chosen likely would not be a former priestess of Nyx, and possibly in this variant Nyx would not be broken and the moon not shattered) could see through a myriad of animal eyes and would operate from the shadows, not like any sort of invading army. Towns and military units, instead of being conquered and attacked, would be steadily raided and gradually overrun. Men would be driven to despair and lose their humanity, giving in to their basest desires.
Troops could include shape-shifters, berserkers run amuck (similar to Firefly reavers), ghouls, a type of corrupted animal predator such as a great cat, blood sacrificing ritualists.
I agree with @arscott that Zora is hard. If I had to do Broken!Zora, I’d focus on blood, destiny/free will, the consequences of failure
Horror themes: Blood, oh so much blood. Blood used in rituals and dark oaths and Faustian bargains. Being put to the test in physically and spiritually untenable positions. Menacing fire. Perverted destiny and prophecy. People broken from terrible experiences, continuing the cycle of violence.
I’d make the Zora the Betrayer the exception (since she always seems to be the exception) and make her the only Chosen to not be broken, but willingly work with the Cinder King. Perhaps even the one that started the Cinder King to start on his path, with the goal for giving the whole world an end boss suitable for the ultimate challenge. She would toy with her victims, putting them through suffering to see, as in the quote from tv show Firefly by Shan Yu, “Live with a man 40 years. Share his house, his meals. Speak on every subject. Then tie him up, and hold him over the volcano’s edge. And on that day, you will finally meet the man.” She would also be willing to share the secrets of blood to those willing to damn themselves with those secrets.
Troops could include blood drinkers/bathers (either undead like vampires or fully human), blood oathsworn, walking flaming undead (either sheathed in flame or discharging flame), the damned who traded their humanity for some type of physical or mystical power, despairers who were tested by the Betrayer with great tragedy and have come out (a bit like Render) angry at the world and the living.
There is less work to do to change a Broken to a Chosen. Probably the best place to start is to start with how the Chosen would affect the story and go from there. Render -> Vlaisim probably would focus on band of brothers type loyalty and what soldiers owe to one another. Blighter -> Elenessa would likely be a campaign full of inventiveness and intricate plans long on creativity and short on brute force. Breaker -> Minika is hardest, mostly in how to both differentiate from the Horned One while still being relevant to a land-based military campaign. My best guess would be to lean into Minika’s past as a traveling protector and warder, so full of stories of how a military order can help civilians, or could struggle with having to constantly leave them behind.