Stage 1 (Totems phase): When dragons teleport to the totem, all players must instantly step a few sqm away, since it’s hard to see who the dragon has as a target. This prevents them from healing the totem. Repeat this every time a dragon teleport towards a totem.
Kill order on stage 1: top left (deal energy dmg) > removes fear, top right (deal phys/death) > removes root, bottom right (deal death/holy) > removes paralyze, bottom left (last one) (deal ice dmg) > removes drunk/triggers stage 2.
When stage 2 begins, all debuffs return (paralyze, drunk, fear, root), so place fire bombs to avoid getting feared into Enthralled Dragons (read more below). One bad fear/root is enough to kill someone.
Stage 2: Do not stand in wraithfire (purple fire), it deals 15% max HP per tick.
The Eyes that spawn throughout stage 2 deal unavoidable agony damage (30%~ of your max hp), so line of sight them if possible without luring dragons. If you must soak the damage, do it away from the group and pay attention to your hp.
Players can get “caged” (teleported to another room) and have to kill their way back to the teleport. When killing Bone Barriers, you can body block it as it respawns to change its spawn location. It gives you/other players one less Bone Barrier to kill later
Most importantly is the 4 Enthralled Dragons that spawn and deal heavy life drain damage. Equip bone fiddle and Necklace of the Deep or Greater Garlic Necklace when entering stage 2.
Safest method is to lure all dragons north together as a team, quickly trap them with magic walls/wild growths, then the whole team runs south to the wall and fully focus the boss. If done cleanly, they might stay north throughout the whole fight. If they do come back, having one on the RP or EK is manageable. Dragons are immune to exeta res, so if a player gets trapped you must rely on random retargeting or the cage mechanic.
Throughout the entire fight, the Bone Overlord randomly drains ~25% max mana over 10 seconds to a player. This is RNG and unavoidable. Maximize boss damage and don't waste too much time on luring away Enthralled Dragons. Some teams have the EK stay to the south wall and use runes to avoid accidentally pulling dragons into the group.
