Edit: Found the answer after a lot of scrolling. Adding it here, because I already posted it below but people are still arguing after skipping most of the comments.
This is probably the most disagreed upon question in the game, so I’m hoping someone has a legitimate source from Blizzard clarifying what can drop in the Great Vault.
There seems to be multiple “theories” about how the Great Vault works. This is specifically about raid slots.
Any item in the raid can drop in any vault slot.
Items will only appear in the vault after killing that boss on any difficulty. **
Items will only appear in the vault after killing that boss on that specific difficulty.
Any item in the raid can drop in any vault slot, but the chances are greatly reduced for bosses you haven’t killed.
I ask for one specific reason. As a BM Hunter, I need to maximize my chances at Rasz bow. Currently, my vault is 3/3 normal raid slots, but my guild raids Heroic on the weekend.
That leaves me in an unenviable position, since our guild is currently 7/8 Heroic. If I have to kill Heroic Rasz for Heroic bow to drop in my Great Vault, then I have a couple choices.
Help my guild kill five Heroic bosses and leave the third slot as Normal and hope for the best.
Avoid killing any Heroic bosses, so I have three opportunities for Normal Neltharax in vault.
Both of these options are a bit toxic. Essentially letting my guild down to increases my chances at a bow that is leaps and bounds better than anything else in the game. If the bow can drop in a Heroic slot without killing Heroic Rasz, then there is no problem. But currently, I can’t find any reliable information about how it actually works, because Blizzard seems to think no communication is the best course of action.
That’s false - they may not have killed it that week, but they must have at some point to unlock its loot - the exception being tier, which you can get regardless
I have 100% gotten non-Razz items (both tier and non-tier) on toons that have literally only ever killed Razz. So I don’t think that killing Razz only will increase your chances of getting the bow.
However, I was under the impression that it doesn’t go the other way—that if you want the higher iLvl Razz rewards, you will have to have killed Razz at one point.
I’m more interested in if killing the boss on any difficulty unlocks it’s loot.
My own anecdote: I’m 95% sure I had Whispering Incarnate Icon in a Heroic slot BEFORE I killed Primal Council on Heroic. I had killed them on Normal though. I say 95%, because I screenshot all my vaults and the file creation date on the screenshot is a few days before we killed Heroic Council.
This would seem to imply it just takes a kill and difficulty doesn’t matter, but I’m not 100% certain.
Tier gear is definitely an exception - I received Mythic tier shoulders prior to even doing any bosses on LFR (and still have yet to kill anything in actual raid besides one heroic boss kill of Terros)
https://worldofwarcraft.com/en-us/character/us/silvermoon/kageriyu tank I run keys with has ilvl 421 (Mythic) version Seal of Diurna’s Chosen they got from vault, despite having never killed that boss on Mythic.
The way it worked in Nathria is you couldn’t get vault loot off Generals or Sire until you had killed Sire once on normal, but after that the loot respected the level of your vault slot regardless of whether you killed Sire on Heroic. The reason I know this is how it worked (besides Blizzard’s initial confirmation back then) is because I looted a Heroic version of Stone Legion Heraldry out of my vault the week after I killed Sire on normal.
It continued this way through SoD and SFO, where I was seeing Heroic loot off the higher item level bosses after having beaten Sylv/Jailer on normal at least once. Blizzard also has not stated that anything was changed.
The only thing that really throws a wrench into this is that there are three item level tiers inside each difficulty of the raid this time around instead of two. But I really just think Brood and Raszageth loot are tied to beating Rasz at least once on normal.
