In Midnight if you collect a tier set, you unlock all the lower difficulty appearances of that set

Coming during Midnight, once a full tier set has been completed, the appearance for all lower tiers of the same appearance will also be unlocked. Eligible sets are noted in the UI. This is something that the community has been asking for fairly consistently and it seems the request has been answered — though it does come with some additional changes to the way that the catalyst will work moving forward, and how appearances are currently collected. In short, you can currently take a piece of tier gear from 4/6 to 5/6 (Hero gear, in this example) in order to unlock the appearance of the next higher up tier set. This was neat, as it meant LFR players could get the normal appearance, and so on, but it appears that will be going away with the new expansion.

Starting in Midnight, appearances will no longer change when being upgraded. Essentially, if you are chasing a tier set using the Catalyst, you would want to use the few charges you get per raid tier on the highest pieces of loot you could get (if that were the appearance you were looking for), instead of using them on equipment upgrades. That’s a rough 16 weeks wait, also not being able to use those charges to possibly get further ahead.

Blizzard understands that as well. Pointed out in the third page of the Alpha notes:

Acquiring a class set 4-piece bonus now unlocks a character-specific Feat of Strength that will enable Catalyst charges to drop from raid bosses, Mythic+, Bountiful Delves, and Rated PVP on that character for the remainder of the season.

What we will need to wait and see is if the drop rate on those additional Catalyst charges ends up being; if it’s too low, then people will continue to hoard their charges, but if it’s too generous… why make the change at all? Just browsing social media shows this topic is a fairly heated debate, and I can only say that I personally am a little saddened that the mythic appearance wont be as easy to reach. If you have any thoughts, I’d love to see them.

[Edit: 10/06/2025] So it would appear that Blizzard has heard the community and has changed their mind on this change! Going forward in Midnight, if you upgrade a piece of gear to it’s max capacity, you will then unlock the appearance of the next tier set up — so go 6/6 on a Hero piece, you’ll unlock the mythic appearance. This is a total win for everyone, so let us rejoice!