making a mob ignore someone with a certain buff

[Dibalamin]

Ok, I'm trying to script something and I have no idea if it is possible. I'm trying to get a mob to ignore people that are affected by a spell he casts.

I see that $mob->FindBuff(spellid) but I'm not sure how to make it work the way I need it. After he casts, i want him to review all possible players in range, suspend the players that have the debuff on the hate list, and then change targets to someone that doesn't have the buff. If all players have the debuff, I still want him to change targets.

Basically, I'm trying to recreate the effect of fear to suspend the mobs attack on someone feared and hit the people that weren't feared.