Obviously a large monster is less likely to suffer from fear or terror itself. There is no way a huge Dragon is going to be scared of a Troll, for example. These special liabilities also apply to any rider of a large monster (or a steed) too, so a Dragon rider wouldn't be afraid of a creature that would frighten him were he on foot. They also apply to units that are accompanied by fear or terror causing creatures: a Skink unit with a Kroxigor would be immune to fear, for example.

The following rules apply:

A creature that causes fear is not affected by enemies that cause fear. Faced with an enemy that causes terror, a fear-causing monster only suffers fear, not terror. For example, a Troll causes fear and a Dragon causes terror. The Dragon is not at all worried by the Troll, but the Troll fears the Dragon.

A creature that causes terror is not affected by fear or terror at all. For example, a Dragon rider is completely unworried by fear or terror because his mount causes terror.

lt sometimes happens that an enemy unit of ordinary Troops is led by a mighty Hero or a monster which causes fear or terror. In this situation, test for fear/terror if a charge will result in the charged unit fighting the Hero or monster in question.

In the case of terror a unit must also test if it is within 6" of the creature at the start of its turn, but not necessarily because it is within 6" of a unit that the terrifying creature is in. If the unit is charging a unit of enemy troops in the side or rear, so that the charging unit won't have to fight a terror-causing monster, then the unit does not have to test for terror. This is common sense - if you don't have to confront the beast then no rest is required.