I am -assuming- DMC:V because the mastery on foul gift is very minor so it hardly increases metamorphosis damage, and it's pretty much useless outside that
Cant confirm/deny, without any math or such i think its a good trinket. If you combine this with moonwell chalice (which is pretty easy) you have 2850 Mastery instead of 1700 to snapshot for Meta and Doomguard. Both of those Trinkets have Int as passive Stat on it, which is too great. Bonus is the Use Effect(5Min CD) which makes more AE damage and heals the you each time for a little amount.
But thats just my personal opinion for now.
If someone with enough knowledge, could calculate it for us, it would be great.