By far the most difficult quest I have ever done. Some quick tips are:

Be dueling a warlock that you trust immensely while fighting Solenor, if you can keep him wing clipped, have aspect of the cheetah up at all times, you don't have to kill beetles. The reasoning for the warlock is for Curse of Recklessness (no fearing from Solenor).

Simone's pet doesn't need to be killed, but you need to loot her head before he kills you.

For Klinfran, if you are specced for Scatter Shot, you can kite to different ends of the Burning Steppes then use Scatter Shot and go the other way. He is leashed to only Burning Steppes, so no Redridge/BRM.

Solenor - A nice little tip for Solenor is when he starts off, drop a explosive trap and have him run into that. Then wing clip him and bolt outta there. The trap should to AoE damage to everything around him, and if you have curse of Recklessness on you, you shouldnt need to worry about the fears, so for the time the explosive trap lasts, you should have no problem with the bugs either. Just unload into him for when you can, but be sure you have a few mana pots on you and a shadow protection pot on you to keep the damage off you. Once the bugs start poping, and your trap wears off, when he's wing cliped git up volley rank 1 when you have all the bugs in a group. this should finish off the little suckers with use of the least mana as possible. This guy was the biggest pain for me personally, but that really just depends on what you're good at.

Artorius - The main problem you WILL run into here, is getting around corners, and mana. So, when you start a turn, any turn at all, be sure to hit him in the face with a concussive shot, but dont get too far ahead of him in the process. Also, keep rank 1 arcane shot out like Kaenos said, and hit him with that every now and then between serpent stings to stay on his aggro list. I only shot him with the sting once every 3-5 seconds, because if you spam him, it will only stack up to 5 times, and your just wasting mana. The main thing to remember here besides the wait time on serpent sting is that rank 9 serpent sting DOESN'T work. One of my guildmates found this out the hard way, and only did minimal damage to him. This may have been updated in 2.0.1, but to the best of my knowledge, stick to sting rank 8.

Simone - Basically easy to kill, i got her pet down first, and the killed her, but as long as you have nature protection pots and some mana pots on you just in case, you should be able to kite her around, even without killing her pet if you want to. Having another hunter follow you around with aspect of nature on is really good, because that allows you to keep aspect of the hawk on, which can really add to your DPS.

Klinfran - Best thing to use here is rank one for wing clip. It gets the job done without wasting mana. The strat here can really be based on your weapon speed. Since each weapon has a specific attack speed (2.4s or whatever) once you scorpid sting him, you run up and attack him for 10 seconds. Your weapon can help time this, because if you have a 2.0 second attack speed, just hit him 5 times, wing clip and start running away. Try not to use raptor strike, because this fight is gonna be the longest one, and you will need the mana. When the fight starts off, hit him with concussive shot, frost trap, whatever you got to slow him down, and once he enrages hit him with scorpid. Then, start the attack cycle of running up, hitting him so many times, wing clip, run away, wait for enrage, and hit him with scorpid sting again. From there rince and repeat for roughly 7-10 minutes. Keep some mana pots with you for this fight specifically, and be sure to have a tuber or two for some health incase you slip up and he nails you once or twice. when you get far enough away from him after wing clipping him, you can hit him with an auto shot or two to add to some damage, but never try to aimed shot him. Also, don't use counterattack if it comes up. Imp wingclip can be helpful, but keep in mind you need to wait 10 seconds after you wing clip him for the enrage to come back up, and if you counterattack him, hes only stuck in place for 4 seconds, so he will be charging at you for 6 seconds, until he enrages, which most likely means hes gonna enrage within your minimum range. The most useful thing to use if this does happen though is scatter shot, then get away from him and hit him with a scorpid sting. You might get hit once or twice, but you should be able to survive 2-3 hits, and then just pick up where you left off and learn from your mistakes.

If you use Snake Trap, the demons will run away.

As an important note, you CAN NOT use your pet during any of the encounters whatsoever. Failed two separate spawns before figuring out when they meant 'alone' that included your pet.

If ANYTHING besides you registers on a demons aggro list, it's game over.

No pets, no snakes, no trinket pets, no engineering tricks, no direct interferance from other players of any sort, nothing. period.