A fear effect temporarily lowers morale by its damage value, to a maximum penalty of -5. This penalty is halved every round, rounded towards zero. Additionally, it adds to the hidden "morale problems" value of the unit and all units in the same squad.
Fear effects come from a variety of sources, including weapons, spells such as aura unit ability. The fear aura ability rapidly fires off invisible fear effects that target nearby squares, but cannot affect friendlies. Fear auras follow the same mechanics as the other auras., and the Fear
Regardless of the number or strength of fear effects and the morale problems values of units in the squad, any given squad may only make one morale check every turn.
Fear comes in two forms. Both versions apply the cumulative penalty to morale, but differ in their ability to force morale checks. The common, potent version used by all other effects adds 1000 morale problems to all squad members, and then adds a further 1000 to the morale problems of the affected unit. The weaker version is used only by the Howling Bows wielded by Ancestor Vessels, and adds 1 to the "morale problems" value of an affect unit's squad, and the affected unit gains an additional +1 to its morale problems.
A squad is guaranteed to take a morale check if any member has a morale problems value that is 10000 or higher. Lower values may cause checks but are subject to more requirements.
Notably, the morale problems addition is independent of the strength (or damage value) of a fear effect, which determines how much temporary morale penalty to add. As such, once the threshold of 10000 morale problems is reached on a squad, further fear effects will serve only to lower the squad's average morale making its check slightly more difficult.
Despite what is claimed in the manual, the area of effect of a fear aura is hardly changed over the feasibly obtainable range of fear values. Like all other auras, it requires a value of 25 or higher to hit further than a single square from the origin, and values instead alter the expected number of squares hit per turn.
However, as hitting any member of a squad 9 times with a fear effect is sufficient to cause the squad's morale problems value to reach the 10000 threshold required to unconditionally force a morale check, additional fear effects beyond this point will serve no purpose besides to lower the average morale of a squad, making additional benefit minimal on an effect which is typically fairly difficult or expensive to stack to high values.
As the number of enemy troops per square is variable, the amount of fear effects required to reach this threshold of diminishing returns is somewhat variable. Additionally, fear pulses themselves are generated at random intervals, and then they may randomly be "wasted" on friendly squares or the user's square. Because of this, the probability of reaching the 10000 morale problem threshold cannot be calculated for general cases.
There are probably ways to calculate the probability of hitting 10000 morale problems in some situations, like lines of troops, or a lone thug surrounded on all sides by enemies, which may be interesting and add some useful insight to this article