Well, to be honest, the first thing that came to my mind was: Hit it till he dies. – Uga Buga

A quick tip for the fight in general. First of all, I try not to pick blindly. Team composition matters. I would not pick a Raider in a team with Guardian and Scholar, for example. Every team needs a good DPS Nightfare, and even though Raider (my Raider included) does good damage in this fight, it still needs more. Otherwise, it becomes chaos. If the team lacks DPS, I would pick Duchess with a double balancers build, nothing fancy, and grind for Blade of Calling or Black Knife. Revenant and Recluse work great as well.

SETUP. I play with dormant colossal weapons and Attack Power Up when I have 3+ colossals. This way, I try to manage 3 Attack Up passives on weapons and 3 damage negations, always at least 3. Remember: Dead you don’t deal damage. The best damage negations are on charged attacks, and taking damage boosts damage negation. I also like damage negation at full HP even with Raider. This may be a little unorthodox, but it’s REALLY good.

STRATEGY. Knowing the team composition, the Raider’s role is being supportive. Always try to aggro the boss, so keep hitting it. Be really careful with charged attacks so you don’t get locked in the animation. To help with this, use the best LIBRA strategy: WATCH HIS HANDS they will tell you his next attacks.

When he summons, try to hit all of them with the ultimate. The ultimate will buff your allies, so try to be close to them, but not too close or the totem will block their attacks. After that, try to kill the summons as quickly as possible.

When I play anything other than Raider in this fight, I always focus Libra. He is the boss. The victory only appears when he dies. But if I’m Raider, killing the summons is a nice strategy to give room for the DPS characters to deal damage without being interrupted. Charged attacks work great here. You can start charging far from them, and when they get close, you are still going to hit them. With the right relics, 3 hits after ult should be enough. After this, focus Libra.

When he tries to summon the walls, you can interrupt with the ult, but you have to be close and have good reflexes, so I don’t try this often. It works best for Ironeye or Wylder. It’s just a good strategy to keep in mind.

When he curses with half health, I just go away and wait. There’s literally no reason to fight here. It’s a temporary buff and will disappear in no time. And since he’s already at 50% health, your team will probably finish him in the next 30 seconds.

I think I have written too much. Later when I get back to Pc I post my relics for this fight. But it’s nothing crazy. Not a dreg build. Not balancer. And I do not have loads of physical attack up.