Can confirm the challenge is kill Oryx with 16 orbs detonations at once. Deaths do not matter. Run through as usual, kill ogres, and knights. Ogres must die in close proximity to the previous bomb. Knights must all die and not be allowed to eat a orb. Repeat four times till each corner has four orbs ready. On the forth orb all chosen plate holders detonate their orbs. Oryx will lose all his health as if you ran through four detonations of four bombs and appear in the front of the room like usual. Kill him and look behind you for double chests. Check my Warlock for proof.