Necromantic Focus (intellect dps trinket from Baleroc, the gatekeeper in Firelands)
States on the tooltip:
Equip: Grants 10 mastery for 10 sec each time you deal periodic spell damage, stacking up to 10 times.
I’ve tested this today and the trinket seems to only reach a max of 29 mastery on 10 stacks of the buff.
This could be a really strong trinket if the equip effect worked properly!
I haven’t gotten the chance to test other timewalking trinkets, It might that this has more applications regarding the Firelands timewalking drops.