On arena one mage was 2 times immune for my fear (not missed) what I do not understand. Started to talk with my arena partner feral and he was saying about spell penetration in case of druid and told me sth what I did not know about before.
He said if he has not enough s-penetration someone can be immune to cyclone every now and again. Is it true? If so, why? Cyclone does not deal any damage which can be supported by penetration.
Spell penetration prevents Resists and not immunity. If you had not spell penetration at all, your fear would occassionaly get resisted. The more resistance to shadow your target has, the more likely he is to resist your fear. By spell penetration you ignore targets resistances, meaning you can eliminate effects of resistances and count only with base resistance to non-damaging effects
Are you sure it was not diminishing returns? I remember Cyclone sharing DR with Fears on private arena server I was playing on, but don’t know if it’s true for WotlkC.