Additional tips: Reddit Thread

If you can, have two 30's with your party. The chances of both of them staying behind are slim. You really do not want any 29's dealing with the relic as Adds will tear you apart. If you are In a situation where a 29 has to pick up the relic, the rest of the relic team helps out. The relic team should always help with the right portal, (some people call it Venus or Past or Green) to take down the Minotaur.

After the relic is brought back to Atheon, you have two choices. Go to the middle Island, or go to the the back where you entered. Both have pros and cons. If you go to the back, you have a much less chance of hitting his by the blast radius of Atheon's projectiles but you will be at an extended range where damage might have a drop off depending on the weapons. Go to the middle and you are much closer but shots tend to hit the platform and the left rock and damage you in the relic cleanse shield. Do the one that is safer for the team based on levels and weapon types. I prefer the middle platform but I have also been obliterated by his shots through the cleanse shield. Your call.

After each cycle, Atheon will detain the group staying behind. Keep your feet on something solid or it will be an instant kill. Try to get on top of a platform so if you have trouble getting out of the detain field, Supplicants will not detonate on you. If you get out before someone else, help them out. If you have super good advice or a gun with Mulligan, the detainment field does not count as an enemy and shots will return to the magazine often.

Supplicant spawns are always right, left, right left. And with three supplicants per wave. They have a tendency to still blow you up if you are on the right platform sync plate. So be careful. Use high impact weapons to dispatch them quickly. Hand cannons, scout rifles. auto rifles that fire slow but hard such as Suros and Shadow Price will also work, but not necessarily recommended. If after a few waves, you are still having a lot of supplicants between cycles, use your Time's Vengeance period to take care of them and clear the field. Ensure your survivability while you are being detained.

Oracles can be a Bitch, especially if you do not have weapons that have oracle disruptor on them. I would say that these are almost mandatory on hard because they spawn so quickly and have around 3800 health when allowed to fully spawn. If you do not have a good Oracle weapon, a fusion rifle (Pocket Infinity gets a special mention here as it destroys them and often returns shots to mag as Oracles are not technically enemies) will work wonders and the relic holder can help out with their super and R1/RB while midair. Using Ground Pound (Jumping and then using R2/RT) on Oracles can be dangerous as you may send yourself over the edge and rarely Oracles will deflect your velocity away from them sending you off the map. Firing on Oracles as soon as they spawn also kills them quicker because they start at about 1200 Health and start gaining it until they hit around 3800. Shoot them as soon as they appear to have them with less Health. (Shooting them stops the health gain, so it is totally reasonable to Shoot as soon as they appear once and reload and then kill.) Once again, guns with Mulligan or SGA will often return rounds as Oracles are classified as objects, not enemies in the game. And make sure to kill the Oracles in order. Focus fire.

Damaging Atheon is probably the most important part of this fight. So lets talk DPS. You already know that Gjallahorn is king. If you have it, use it. Nuff said. Moving on. The Heven Vengeance does 12% less damage than the Gjallahorn but is the second for burst DPS. The Truth is not comparable as it does 50% less damage than Hezen and 66% less than Gjallahorn. Either you use Hezen or Gjallahorn or you use an HMG. The Thunderlord, SGA, Swarm, Culling, and Zombie apocalypse are all good for this fight, I prefer the Thunderlord because shots eventually get more accurate but the Swarm is a close second. A total HMG ammo reserve does about 250% more damage than a rocket total reserve, obviously over more time but 250% is something that cannot be ignored, especially if you land all your criticals. If you have an Ice Breaker, use it. If not, use a fusion rifle. Fusion Rifles hold more ammo than sniper which extends their use beyond damaging Atheon and do between 6000 to 8000 per burst depending on Impact. I prefer the Wizard 77. Pocket Infinity gets a special mention here because it has great impact and if you aim a little to the side, you have a pretty good chance of shots returning to mag to keep damage up. Primaries all go down to preference and which will help you more with Oracles and Supplicants. As long as you can hit the juice box consistently, the damage will add up, very quickly with AE, VoC, FB, hell; Even Preadyth's Time piece does well on Atheon. The key here is just doing as much damage as possible to Atheon in each cycle. Use your Primary, then your special, then your heavy. Go down the line as it is faster than reloading.

ProTips: Never Chuck grenades at Atheon. Grenades are not effected by Times Vengeance and make Atheon move, messing up everyone's shots. Seriously, no grenades.

Defenders can use Armor of Light to tank two successive Detonations from Supplicants.

Drop weapons of light behind the cleanse shield for super awesome damage.

Warlocks, switch your class to sunbros and save your super for when you go down. Using your super also makes Atheon move and the damage comparison versus your guns does not justify it.

Never really use your super on Atheon. Save it to help You through the next cycle. Including you, Gunslingers.

Leave your cleanse shield at about 3 seconds to get to a safe place for the next cycle. Relic holder should call this out at 5 seconds for everyone to prepare.

If one person goes down, keep going. If two people go down and Atheon is not close to being dead, wipe. If you died, use up and down on the Dpad to toggle people and scout for them.

If only two people get sent back, open the portal quickly and send one person in IMMEDIATELY to help.

If you are about to succumb to the Oracles, wipe and retain your super energy.

Keep it lighthearted and keep morale up. If things are not working or a person is having short longevity, watch them. See what they are doing. Teach and advise. Not dictate and overrule. Come together as a team and fix each issue. If you can do two cycles fine, you have mastered the boss fight. DPS is THE most important thing in this fight. That and staying alive, but they kinda go in hand because dead DPS is no DPS.