[K]

Horror marking comes in "levels". Ok, most people know that.

What they don't know is that only some effects have the capacity to increase a horror mark to the next level. The spell Horror Mark seems to either not increase a mark's severity, or it has a very low chance.

The Forbidden Light seems to increase Horror Marks quite quickly, though. I've never increased a Horror Mark past the point where each turn its "one Doom Horror, then a Horror, then another Horror", but it might get worse.