IMPORTANT NOTE: For many specs (and for Mistweaver specifically), covenant balancing has been shifting constantly and it might shift again. However, seeing as all Covenants for Mistweaver are relatively close to each other in the current state of Beta, there is a chance things will remain the same as they are now.
ANOTHER IMPORTANT NOTE: Like stated in the previous paragraph, all Covenants are very close to each other in terms of power. Outside of absolute min-maxing, feel free to pick the Covenant you enjoy the most.
Necrolord is an incredibly strong pick for Mistweavers in raids. Bonedust Brew is a great ability which provides a fair amount of extra free healing. Being on a 1-minute cooldown by default (and there is a possibility to reduce the cooldown even further with conduits), it fits most of the damage patterns in Castle Nathria really well, especially on later bosses. On top of that, picking Necrolord gives us the access to Emeni - an incredibly strong soulbind due to Lead by Example trait, which gives a large amount of main stat to us and a smaller amount to our nearby raid members whenever we cast Bonedust Brew.
Like I said before, Emeni The Slaughter Daughter is one of the main reasons the whole covenant is very competitive. Lead by Example is an absolutely amazing trait, which after recent changes is available straight away after unlocking the soulbind.
After receiving a 97% nerf to Weapons of Order ability (though it got buffed later on) and a 96% nerf to Strike with Clarity conduit, Kyrian still looks like an extremely solid choice for raiding for Mistweavers. Kyrian will be your choice if you really like Fistweaving as it makes Invoke Chi-Ji, the Red Crane much more potent, but even outside of that synergy Kyrian is extremely close to Necrolord in terms of power, while being a more versatile choice, which works with all talent builds. As for soulbinds, Pelagos looks like the better option compared to others at the very early stages of the expansion, while Kleia becomes a better pick later on.
Currently, Pelagos looks slightly better compared to other options, at least early on until you will have enough Renown to unlock all traits. Combat Meditation provides a nice mastery bonus after you cast Weapons of Order. Kleia used to be competitive but after recent nerfs to Valiant Strikes (1 minute CD and you get stacks only from your own Critical Strikes), this soulbind looks rather weak, however, once you get access to the last row, Pointed Courage provides some insane value, which will make Kleia superior.
Mythic+: Kyrian / Necrolord
In Mythic+, both Necrolord and Kyrian are slightly ahead of Night Fae and Venthyr (however, as stated before, they are not very much behind and still remain very reasonable picks if you wish to do so), and Kyrian has a slight edge over Necrolord. The reasoning for this would be the fact that Chi-Ji is a very solid pick for dungeons and as mentioned earlier, Weapons of Order empowers our Crane friend by a fair amount, and also because how Bonedust Brew loses a bit of its value in a dungeon setting. However, Necrolord can still be quite useful and provide some extra damage and healing, which is always great to have.
Soulbinds and Conduits
Potency: Jade Bond
Slightly increases the healing done by our Celestials and reduces their cooldown every time we trigger our Mastery healing. Based on my experience on Beta, you can generally get around 20-25 seconds of cooldown reduction, which can be useful depending on different bosses’ damage patterns. Overall a very good choice.
Potency (if Necrolord): Bone Marrow Hops
Provides a solid increase to Bonedust Brew’s power as well as allows us to cast it more often meaning higher uptime of Lead by Example. Earlier on the Beta you could even maintain 100% uptime of the buff, which got fixed and now the CDR provided is capped, however, it doesn’t make the conduit much weaker. One of the best Potency conduits available.
Potency: Resplendent Mist
Provides a nice boost to our Mastery healing and makes chasing Essence Font HoTs more valuable. Not a bad choice at all, but two options mentioned above provide a bit more value in my opinion.
Potency: Rising Sun Revival
Will provide around 10-15 seconds of cooldown reduction on Revival if you cast RSK on cooldown. Generally, considering that Revival is not a great spell by itself, and cooldown reduction is quite small and situational, this conduit is not the best choice.
Potency (if Kyrian): Strike with Clarity
Was carrying Chi-Ji build previously due to enormous amount of extra Mastery you’d get, after the nerf it's quite underwhelming: Weapons of Order duration by default is already longer compared to Chi-Ji (30 seconds to 25), so the increased duration part doesn’t matter too much, and the amount of Mastery you get now is extremely low, which makes the conduit very weak. However, it’s worth keeping an eye on it in case it will get buffed in the future.
Endurance: Fortifying Ingredients
The best Endurance conduit we currently have the access to; it provides a nice absorb after casting Fortifying Brew.
Endurance: Grounding Breath
Underwhelming compared to Fortifying Ingredients, but better to use than other options in case you have 2 endurance slots for some reason.
Finesse: Dizzying Tumble
Not by any means groundbreaking, but gives a nice damage reduction from enemies affected by our Leg Sweep for a short period of time. Important to note, that the effect is activated after the stun duration has expired.
Finesse: Swift Transference
Whenever you only have enemies that are immune to stuns, use this. The effect is almost negligible, but it’s better than other options (read as nothing).
The best legendary for raiding currently is Tear of Morning. It empowers our Vivify cleave healing by quite a significant margin, as well as making Enveloping Mist healing cleave in the same manner. Provided that we are already encouraged to cast Enveloping Mist in the raid a lot more because of the new Celestials and Enveloping Breath, this is a very nice bonus and is currently better than other alternatives. An important thing to note is that this legendary’s performance is somewhat inflated by the bug it currently has (Enveloping Mist cleave component triggers Gust of Mist which probably is not intended), however even without this bug it remains a very powerful choice.
Invoker’s Delight - Gives a big haste bonus for 20 seconds after summoning your Celestial. It can provide some big value since all healing from Enveloping Mist and Enveloping Breath scales off haste. Definitely a solid option, but with the current tuning Tear of Morning looks a bit better.
Ancient Teachings of the Monastery - A decent option for Fistweaving. An important thing to note - the buff is gained after Essence Font channel ENDS, not the start, but cancelling the channel or getting CC'd during the channel will give you the buff regardless.