I have made a small Fightclass as I was not happy with any of the other shadow priest fight classes. For some reason, they would constantly try to move forward whilst casting which would mess up the rotation and look risky . So here is a very simple fight class which just dots and focuses that target. Drop any high expectations, because this is as simple as they come -- without looking like a bot and getting you banned.
Auto Shadow form
Auto Inner Fire
Auto Power Word: Shield -- before engaging combat
Auto Vampiric Embrace
Auto Divine Spirit
1. Vampiric touch -- Will not cast twice!
2. Devouring Plague
3. Shadow Word: Pain
4. Mind Blast -- whenever off cooldown
5. Mind Flay -- if the bot has nothing else to do
6. Shoot Wand -- if mana is so low the priest cannot cast anything
Shadow Word: Death (highest priority) -- Will attempt to steal the killing blow when enemy has 1,200 hp.
Shadow Fiend -- when mana is getting low
Silence -- Only when enemy is casting
Psychic Scream -- with range check
Psychic Horror -- But only if the target is within combat distance
Hope this helps!