Originally Posted by
Vaeoth
After gemming, enchanting, and grabbing the right pieces of gear the most important difference between good shadow priest dps and bad shadow priest dps is "rolling/weaving" your procs into your dots. Let me explain and it will become clear how this relates to trinkets and your mastery confusion.
When we cast Devouring plague, Vampric touch or when sw:P is refreshed by mindflay, wow looks at your spell power, haste, and crit you currently have and applies them to these dots for their duration. So if for example your a tailor(shadow weave cloak), engineer(synapse springs on gloves), have power torrent on your wep, darkmoon card volcano, and Theralion's Mirror you have a lot of procs you can roll into your dots to make them more powerful.
Lightweave embroidery - 580 int
Synapse springs - 480 int
Power torrent - 500 int
DMC Volcano - 1600 int
T's Mirror - 1926 Mastery
Now I haven't done the math on when its worth it to refresh dots when x procs, however it does seem pretty clear that when you have 1600 int proc you should refresh dots also DMC volcano shares an internal cd with power torrent. This means they usually proc around the same time with some rng mixed in there.
To answer your question as to why a 1926 proc on a trinket is so good when its not weighted that high in our stats. Our mastery directly affects our dots with empowered shadows buff. So when we are looking at trinket procs we need to weigh the benefit these stats give to our dots over the benefit to other spells like mf mb and sw:d because we will be using our dots during these procs. This changes stat weights and priorities for trinkets. Dots are even more heavily weighed when it comes to trinket procs due to the fact that we can refresh dots when the trinkets first proc and then refresh them again when the proc is about to wear off. This increases the time we gain the bonus from the trinket by an extra whole dot time. Big dps increase.
So this is where theralion's mirror gets its awesome rating. If any of you shadow priests are looking to push the envelope of your dps and really shine this is probably an area you can improve. I would consider weaving your procs into dots to be the "Art of Shadow"