First of all, make sure atleast 2/3 people have the Particle Disruptor mod from the Artifact. It takes 1 special fusion shot or 5 Linear fusion shots to activate and is a necessity. Someone should use [b]Divinity[/b]. Everyone else should use a legendary special fusion rifle, preferably a [b]Cartesian Coordinate[/b] with Vorpal weapon or the [b]Null Composure[/b]. If you have another rapid fire frame fusion that will work too. Dont use any other type other than Rapid Fire Frame fusions. For the heavy Weapon, Any linear fusion with Vorpal Weapon will work. I would recommend [b]Threaded needle[/b] or if you play trials the [b]Reed's Regret[/b]. Use Boss Spec mod on EVERYTHING. If any of you have [b]1 Thousand Voices[/b] I would recommend that over any heavy weapon. When the 30th Anniversary update comes out they are buffing [b]Sleeper Simulant[/b] by 16% so then that will be a VERY good option for damage. Now for your build, Use [b]Thundercrash[/b] with [b]Curiass[/b] of the falling Star and just keep hitting him whenever you get your super back during the fight, should be 1 or 2 during 1 phase. If you dont have that then use any Solar Super with[b] Fusion Nades[/b], and use the [b]Exotic Ashen Wake[/b]. Throw the nades whenever you get them back for about 100k per nade. Also make sure if you can have a [b]Warlock Well[/b] and [b]Titan Bubble[/b] for the extra damage they give. where you stand is important too. Use the stairs leading to Atheon on the other side of the portal if you dont already. Also the 3 people inside Athoen's room shouldn't wait for the 3 who got teleported to start damaging. Once the last oracle callout goes out all 3 of you who didnt get teleported should be near Atheon preferably on something high waiting for the 30 second damage timer to start. Once it starts thundercrash or throw a nade and start damaging. Hope this helps.

Ashen wake Titans on mid Sunbreaker go crazy.