Opening rotation:
Prepot > VT as the tank is running in > SWP > DP > Mind Flay until orb > MB > (Procs should be up now) Refresh VT + DP > Shadowfiend > Archangel > continue with normal priority system.
Normal priorities:
1) Shadowfiend on CD, or if you have procs that are about to come off ICD save it. Only save it if it's gonna be a wait of a few seconds or less.
2) Archangel if dot's have enough time left to get 5x Evangelism before needing to recast. Otherwise, recast dots.
3) Maintain VT uptime (re-cast any time after about 4 seconds left on it, the duration of the next one becomes extended if you do it in that timeframe).
4) Maintain DP uptime - can be re cast whenever as Imp DP beats Mind flay in DPS. However, it's impossible to spam because of mana issues.
5) If boss is below 25%: Double-tap Shadow Word: Death
6) Mind blast on cooldown.
7) If you are low on mana, Shadow Word: Death.
8) Mind flay.
While moving, use Devouring Plague and Shadow Word: Death if you need mana.