Just rolled blood dk, need a few advices

[Asasyn]

never played blood so need a few tips please
1. I have a few trinkets - which one would be the best?
a) 885 ilvl stack stick (strenght + versality)
b) 860 chronoshard + 885 neck for the set bonus
c) Darkmoon card immortality
d) talisman of cragshaper 875 ilvl with socket
d) majordomo bell/memento of angerboda

Always having dilemma about trinkets...what should i be looking for? Im doing a lot of mythic + (especially MoS farm between 8-13 keystone level)

2. How valuable is blood mirror in m+? I know bonestorm can be very strong during fortified but that about the first one? Any particular boss/mechanic/situation where i can preactively cast it and expect some fireworks?

3. Rapid decomposition seems very underwhelming...i want to do some 15+ this week to test myself, would spectral deflection be good during tyrannical affix?

4. How strong is 2pc t 19? I could drop -20 ilvl, lose quite a lot of haste as well, would it be worth of it?

[Revofevi]

Imo Blood is the single best tank for M+'s if played well so welcome to the winning side of DKs.
1. Trinket-wise for M+ you generally want to roll with normal dps trinkets, so any combination of your 860 chrono, 885 vers stat stick, and memento. Definitely use chrono with the set bonus.

A good memento is nice to have as bdk, considering you hardly ever die... so in the case that your entire group dies you'll just be going god-mode with all the procs and still be alive by the time they released and ran back lol. Your talisman could potentially be useful on tyrannical week with certain bosses, otherwise I'd keep it in your bank.
A few trinkets I like to play around with for M+'s are the Ravaged Seed Pod from Nythendra, Ember of Nullification in BRH, and Horn of Valor.

2 + 3. I typically use blood mirror on Tyrannical week depending on the dungeon and how high the key is, anything +15 and above I use Purg just in the case that I royally fuck up a mechanic/manage my cooldowns poorly and need saving. Anything +10 or below, Bonestorm is the way to go. A few bosses I do like using blood mirror on are Walord Parjesh (intentionally tanking a spear and using it), Oakheart in DHT (Crushing grip), and Smashspite in BRH (during Brutal Haymaker phase). Idk if it does that much damage but it definitely feels like it.

As far as RD vs SD goes, you'll definitely see a noticeable difference with the amount of RP you're generating during trash/boss fights with SD and it'll feel like BDK before 7.1.5 where'd you're endlessly trying to keep boneshield stacks up for certain bosses. It'll be useful for +15s or above on Tyrannical, especially for bosses where their autos are constantly dealing more than 25% of your HP. SD feels alot more viable when you have the 4pc T19 with below 30% haste.

4. The 2pc set bonus is definitely strong and you'll feel like you're generating alot more RP with it. I don't know what your gear looks like/what haste % you're at, but I'd probably wait on getting the 4pc if you're dropping that many ilvls and work towards the legs, chest, n shoulders.

Hope I helped out, and have fun grinding them Maws.