As Water Elementalists, these demons use Deep Freeze, which can deal 100+ damage and snare bunched-up party members (i.e., henchmen and heroes) in a hurry. Ice Spikes can also deal a surprising amount of damage, especially if many of these spells land at once, causing a small spike. Exacerbating this fact is that these monsters frequently appear in groups of 2-4. Damage mitigation via interrupts, damage reducing spirits like Shelter, and protective enchantments such as Spirit Bond are recommended when fighting multiple Rains of Terror.
Blurred Vision cast by Rain of Terrors lasts for a fairly long time. Players should try not to depend heavily on attack damage when fighting against them and depend on spell damage instead. Melee damage is even worse since these demons have two spells that slow down players' movement. Hex removal is also very useful when fighting them.
The name of these monsters may be a reference to the "Reign of Terror" period of the French Revolution.