As almost everyone assumed, Crota’s challenge is exactly the same as the Warpriest. While this is annoying, the fight is a little different, but not different enough to cause a problem. With that being said, the Deathsinger is much harder, so if you finished that you can finish this.
For this fight I strongly suggest using Gjallarhorn or a rocket of equal power, classes that generate orbs and at least one Gunslinger with Nighthawk. It’s also helpful to have health regeneration when picking up orbs on, but it isn’t required.
No one can pick up the sword twice. For those worried about failing this challenge, Bungie finally made it so a notification appears, see above, when you screw up.
Start by standing next to the crystal and wait for Crota to appear. This will cause enemies to spawn outside this room that you need to kill. Knights can still get through the barrier and damage you, but Bungie was kind enough to remove the ability to damage enemies with Arc Blade. At this point you want to generate as many orbs as possible.
Wait until all the enemies are dead and select someone to get sword and two people to shoot knights. Bungie removed the ability to hang out on the ledge, so you need to do this the old way. The people shooting the knights will spawn wizards when both die that you need to kill. They don’t take long to kill and it works better than keeping one knight around.
Like always, the Swordbearer appears under Crota and will die after some damage. Next to him is the chalice, an item used to heal you since health regeneration is disabled for this fight, which you’re safe to pick up if you’re doing challenge mode.
When the sword holder is ready, have them call out and shoot Crota. His shield has much less health this time, so you don’t need 12 Gjallarhorn rockets to bring him down. You could honestly do it with two, but still fire at least one.
Crota will kneel and you can damage him with the sword. Get however many hits in and when he does his next animation flee. Crota is immune to damage when he has his aura, see above, so wait for it to go away before attacking. When Crota stands up he will spawn an oversoul, which you need to destroy and should be done immediately after bringing Crota down a second time.
This is extremely important. Wait until Crota stands back up to destroy the oversoul or another will spawn. If you’re having problems destroying it, Golden Gun with Nighthawk destroys it in one hit. It’s strongly advised to have someone just Golden Gun it when it’s safe to remove all the difficulty.
After the second time, hide in the starting area. Crota will run to the right, wait and then run back. Repeat the previous steps and the fight will continue. I strongly advised not trying to defeat Crota in two swords, but I do think it’s still possible.
When Crota run to the left side, you want to go to the building to the left or right of where Crota starts. There an ogre will spawn, which you can quickly kill and then kill the other by exiting the room.
For the last bit, simply repeat the previous steps, with a different sword user and the fight will end. Crota will also enrage, but it doesn’t mean anything at this point.
Those who accomplish this on hard should get a normal drop, two ornaments, one legendary engram, Soul Extracted emblem and an exotic primary. No one in my group failed to get an exotic in either challenge, so they’re either guaranteed or absurdly likely. Those who use the Eao item will get another STANDARD drop.