This is a favourite for most Priest players and mostly used in PVP, but is just as viable in PVE as you would expect from a DOT Spec. Below we have an image of the Best Shadow Talent Build to use in WoW Classic Patch 1.12 and is meant for PVP Battlegrounds use. some of the key points with this build are the obvious ones being Vampiric Embrace which heals you for the damage you do, and then there is Shadow Form which gives you a buff that increases Shadow Damage by 15% and reduces physical damage you take also by 15%
Possibly the most complicated Addon I have ever used it is also one of the most powerful. You can build custom Visual and Audio warnings for virtually any situation in the Game. I have used it for Buff Stacks Low HP and Ability Cooldowns many times over the years on various Characters. Blizzard added similar Visual Warnings in Cataclysm.Git Repository: