Eclipse

Don't let everyone's comments about how easy this is make you overconfident. Even as a level 100, you'll take a serious amount of damage that can be potentially fatal if you aren't keeping an eye on your health and using whatever dmg mitigation and self heals that you have.

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• Whack Benedictus down to 50% or so in health to make him cast this irritating shadow spell that turns everything purple.
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• At this point, you must run OFF the center platform and run all around it targeting the various sparks that spawn.
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• Kill ten of the sparks.
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• You may now safely down Benedictus for the achievement.
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Very easy achievement, perhaps the easiest of the new 5, imo.

Once Benedictus enters his Twilight phase, about halfway through the fight, Twilight Sparks will spawn around the room, some can be melee'd from the inner platform, others you have to use ranged abilities or walk down to hit, just make sure not to stand in the bad stuff on the ground for too long at once, as the damage from it stacks up.

We got it on our first try without much extra effort, just requires a little bit of running around before you kill him off.

GL!

If anyone is trying to do this achieve in Legion still here are a few things to keep in mind from my own experience.
1. You have to get the boss to second phase. So you can't 1 shot him
2. You cannot use the soft foam sword toy here.
3. You have to kill 10 adds in phase 2 and then kill the boss to get achieve.

I did the following as a BM hunter:
Stripped naked, equipped weapon and one piece of clothing because I found I needed the stamina. The second phase has a constant damaging effect. If you are naked, you are going to get hit really hard. So, I found that I need a little more stamina and with my Exhilaration heal, healing potion, and pet's spirit mend ability I was able to survive the second phase. With more or less healing your mileage will vary. Remember though that the more gear you have the harder you'll hit and the more chance you have of killing the boss in the first hit. So, start small.

good luck!