If you don't know the new challenge mode got released today and the first challenge it the warpriest. If you want to beat him and earn the awesome rewards like the 320 artifact and the new emblem and a change at a 320 exotic then its time to bring him down.
If your having a hard time passing it or just want to see how its done I've made a video detailing the challenge an rewards enjoy.
https://youtu.be/Y24JMqVnOXY
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It doesn't seem like a challenge..... Only a challenge if you such I guess.