The Coiled Altar
The Intermission of the Coiled Altar encounter starts with both Malacrass and Zul'jan at 0% health. Malacrass uses Ghastly Regeneration and heals both Zul'jan and himself every second for 35 seconds. During this time, Malacrass is immune to damage, but Zul'jan can be damaged and takes double damage. This is usually when raid groups will use Bloodlust and all cooldowns to remove as much health as possible in preparation for Phase 3.
Zul'jan heals for a set amount over the course of the intermission, but when players overgear the content, such as a Mythic raiding group going into Normal, this can result in Zul'jan's health hitting 1HP during the phase. If Zul'jan's health starts at 1HP at the start of Phase 3, there appears to be a bug where Zul'jan is completely unkillable and will remain at 1 HP until you die.
Until this bug is fixed, you may want to stop dealing damage during the Intermission to avoid getting Zul'jan's health too low. Alternatively, consider using Bloodlust in Phase 3 to kill both bosses faster instead.
