Fear/Snare Aggro on Immune NPCs
 

I have noticed that fear/snare will not generate aggro on NPCs that are immune to those spells. On live I was always able to use clinging darkness and fear spells to generate aggro equal to a resist of the spell on NPCs that were immune.

On live when casting this kind of spell against an immune mob, you would have two messages: the 1st one saying your spell has been resisted, then a 2nd one informing you that the mob is immune.

So I guess it indeed gave as much aggro as a standard resist.

I've noticed this on my bard as well in Sky. My first time kiting there I tried spam casting snare song to get agro off somebody and the mob completely ignored me.