The Dauntless One

The Affinity Breaker set is built for this fight or rather this fight is built for you to be able to take advantage of that set. The new revamp of the set just made it that more potent. Since Ruarc will be the target of the Enfeeble debuff  most of the time, you won't want him to land a bunch of weak hits to add to the Shade meter. This set will allow him to hit less weak hits throughout the duration of the fight. He won't be adding much DPS anyways so you don't want him being a detriment.

This build should be built with as high Critical Damage as possible, to ensure that the boss will target Greenwarden Ruarc even when he doesn't have a Taunt buff up. This set will also help with boosting up that stat. Make sure you also build up enough accuracy to be able to land his Decrease Attack debuff from his A2. I put Critical Damage as the two piece set but you could use anything like Perception if you need to.

I went with Refresh for the accessories. You could go Revenge for counterattack but you will probably add Shade stacks from time to time instead of decrease them but it can go both ways. This is so you can, potentially, get the Taunt buff up more often, since you won't have Lasting Gifts to add any extra ticks to the duration.

* Some artifact sets have upgraded versions available. If you have a better upgraded version of this recommended artifact set, definitely use that instead.

This is more of a slow defensive type fight at the highest stages meaning many of your champions won't be built for damage but more for sustaining damage over time so you can safely and successfully win the fight. The blessings reflect surviving and providing a miniscule amount of extra damage to help facilitate the bosses demise. Although you could forego the damage for extra survivability from the Support tree.

For that we went down the Offense and Defense trees. Remember you will need accuracy to land debuffs normally from Ruarc but many of the mastery enhancements from the support tree that would normally be great would go to waste since his passive ability to provide Shields will be locked out most of the fight.

You're going to want to be the target of the Enfeeble so make sure to grab more Crit Damage from Keen Strike. I just went down the left side of the tree, all the way down to Warmaster for some extra damage. You'll be getting lots of heals/Shields throughout the fight so we got Rejuvenation for that. You will want to mitigate the boss damage and many of the Defense tree masteries aim to do just that.

We end with Cycle of Revenge for extra Turn Meter to help get/keep Taunt up. Plus retribution for a counterattack to decrease those Shade stacks when the boss happens to hit hard enough. All-in-all you just want Greenwarden Ruarc to stay alive and keep soaking up all of the bosses attacks. While providing some tiny bit of extra damage throughout the fight or at the very least to stay out of the way and not cause any extra detriments to occur.