General Mechanics:
Thunderstorm - targets random players, tracks target, after a short duration deals AoE on target. May also target ground. The ground target ones will drop an orb. Damage from this ability breaks 'Seduced' from Chaos Strike.
Thunderspark - melee AoE, moderate damage, but kills Chaotic Strike targets.
Orbs - Eat 3 to give a shield for a minute that prevents you from dying to Shock Strike, otherwise it does like 17k damage and goes through Hallowed. Building shield also removes tether. The more orbs are out, the more damage Thunderstorm deals. Managing shield duration is the tank swap mechanic. Eating more than 3 will give an 'overchaged' shield that reduces healing per stack but still blocks Shock Strike. Caps at 3 stacks.
Chaotic Strike - Fears 2 players not top enmity after a short duration. They will walk slowly towards Ramuh then get killed by the melee AoE Thunderspark by Ramuh if Chaos/Seduced is not broken by Thunderstorm. This is a team coordination mechanic, think T8 ballistic missle.
Grey Arbiter - Add, just kill them all to not die to Judgement Bolt. Does low damage across the field. They also have an ability that fires at Ramuh that lowers the time left until Judgement bolt, so kill them sequentially.
Judgement Bolt - Negligible damage if all adds were killed, otherwise 30k and you die.
Rolling Thunder - Links two players together, puts a dot debuff as well as deals damage on any action. 1 person linked needs to eat 3 orbs to break. Can be the target of Chaos Strike.
Phases:
100->66 - Thunderstorm and Chaos Strike management.
65 - Adds spawn. Ramuh will need to be rotated to face away from the group as adds are killed. Thunderstorm and Chaos Strike persist.
Post Judgement Bolt->0 - Introduces tether mechanic. Thunderstorm frequency increases. At 29, untargettable adds spawn that just deal a little extra damage.
So the general approach is save people that get hit by Chaotic Strike and keep the field clear of orbs unless needed to deal with something. Bad phase pushes are possible like in T7; his attack pattern is reset on phase change so you may get a double Chaotic Strike. Also theoretically possible to solo tank, but timing is incredibly precise and not worth it except to say "I did it".