The Nights of Horror actually has little to do with Sheng Seleris, just his people, the Pentans.
You see, at this stage, the Star of Pain had already been slain by the Red Emperor and the Carmanians in the Battle of Kitor.
But, the Pentans never truly gave up their claims on the Redlands and Oraya. They kept travelling through the lands, raiding the Lunar settlers, and herding their herds; until the whole place was overrun.
They grew to be such a problem that the Lunar armies were sent in to drive them back. Which may not have been a wise move.
In the worst battle since the Dragonkill, 150,000 soldiers, magicians, and demigods traded death for death. The Pentans had hired the sorcerers of Orathorn to aid them, and the might of their combined strength caused the Red Emperor to call upon the dark side of the Red Moon's power.
Chaos.
The Orothorni unleashed their own secret magics, and the battle became a slaughter. Things appeared that should not be, the Emperor's daughter, the goddess of maize, Hon-Eel was herself killed when trying to save her siblings from some of the horrors.
In the end, the Pentans were defeated, their army destroyed. The few survivors limped home after arranging peace with the Lunar Army.
Although technically not the Red Emperor, who'd also perished in the chaos.
Believed dead by the Empire, he returned in a new form, with a new face, in a small town in his Empire. He then went to Glamour, and proved he was the Red Emperor. (And deposing the High Priest of Yelm they'd sought to elevate to the role in the process)
He spent the following years rescuing the souls of those who'd been killed in the Nights of Horror. Which brought a lot of respect from the living kin of those unfortunates.
Of course, this also had some ramifications. Some of the nomads who still lived in the Red Lands would in the future rise up in rebellion against the Empire. Including a young Aelwyn.