Bab 257: And Now There Were Three.

Meanwhile, Aeternus was having a field day at the fortress. This group of demons is tougher meat, but meat nonetheless. They resisted even though it was ineffectual. They resisted because it was all they could do. Black flames enveloped them. It had robbed them of their senses and it was still trying to kill them. 

Still, they resisted. They burned through mana trying to keep off the corrosion. The corrosive property of the chaotic flames is their immediate threat. If they don't hold it back, they will lose a lot of their essential body mass to it. It is not the kind of weight loss that anyone will appreciate.