With 500+ average ilvl and a whole-day attempts, I should admit that there is huge difficulty gap between Horridon and CoE. If Horridon is only "too hard", then CoE should called "nearly impossible". Yes, it is impossible for a 500 ilvl 10m team who can easily farm 8/16H in 5.1. Even we did everything without any mistake, our healers would go OOM at Sandcrawler's 2nd activation.
Don't think it is fair to design a 10m boss with nearly same damage, same interrupt requirement, same add number and CC requirement as 25m. In 25m u can have 2+ melee to stick on Sandcrawler to interrupt, or even have one more tank to focus on dealing the living sand or frostbite, not mention that 25m have more damage reduction arrangement. I have also heared that 25m CoE is a joke too.
Yet there are 2 bugs in this boss:
1. When Kazra is actived. He may charge and stun himself continously even when more than 25% of his health dropped. And before his stun expires, he will use dark energy to continously AOE the team.
2. It is said in the text that the Dark Energy AOE is increased by 10% per sec (that should be 10k at first sec, 11k at second sec, etc...). However from the battle record we can see that the AOE damage is 10k at first sec, 20k at second sec. It is a 100% increase. Is it a dungeon journal text error or the damage increase amount is wrong?
All in all, the annoying bugs and more than strict requirement in operation make this boss over tuned in 10m.