There are two Godskin Apostles and Godskin Nobles fighting alongside in Elden Ring's Godskin Duo boss encounter, one of the hardest and most notorious boss battles in the game. In Crumbling Farum Azula, you'll face two enemies at once, each with their own aggressive and unique attacks. Here's a guide to defeating each one.
Location
•Crumbling Farum Azula: This is an ancient, crumbling city that's floating in the sky, accessible later in the game. You'll get to this area as part of your quest to become the Elden Lord.
Understanding the Fight
•Shared Health Bar: The Godskin Duo, consisting of the Godskin Apostle and Godskin Noble, share a health bar, but each also has an individual health pool. Defeating one temporarily can make the fight easier until the other resummons its partner.
Preparation
•Summoning Help: Use Spirit Ashes like the Mimic Tear, which can be incredibly effective as it duplicates your build, providing significant distraction and damage. Alternatively, summoning real players or NPCs like Recusant Bernahl can also help manage the fight.
•Sleep Ailment: Utilize sleep-inducing items like Sleep Pots or Sleepbone Arrows. Putting one of the duo to sleep gives you a window to attack the other without interference or to set up for a powerful combo.
Build and Equipment
•Bleed or Frost: These status effects can be very effective against the duo due to their large health pools.
•Comet Azur with Terra Magica: If you have access to these spells, setting up a situation where both bosses are asleep can allow you to melt their health with this combo.
Boss Strategy Tips 
•Use of Spirit Ashes: Summoning spirits can be crucial in this fight. The Mimic Tear Ash Summon is often recommended because it duplicates your build, providing significant distraction and damage. Other useful summons include those that can put enemies to sleep, like Dolores the Sleeping Arrow, or summon multiple allies like the Greatshield Soldier ashes.
•Exploit Sleep: Utilize items or arrows that induce sleep. Putting one of the bosses to sleep allows you to focus on the other, significantly reducing the chaos of the fight. Sleep Pots or Sleepbone Arrows can be very effective for this strategy.
•Environmental Tactics: Use the pillars in the room to block attacks, especially the Godskin Noble's rolling attack. Positioning yourself so that a pillar is between you and a boss can give you moments to attack or heal.
•Focus on One Boss: Although they share a health bar, focusing on killing one at a time can make the fight more manageable. However, remember that the remaining boss will eventually revive their partner, so use this time wisely.
•Dodge and Timing: For the Godskin Apostle's aerial attack, sprint away and dodge at the last moment for an opening. When the Noble prepares to roll, it's often better to run away rather than trying to dodge through the attack. Learn the timing for dodging their black flame attacks; dodging towards or sideways at the right moment can avoid damage.
•Status Effects: Bleed and Frost are effective against them due to their large health pools. If you have access to the Hoarfrost Stomp Ash of War, it could be beneficial despite its nerf.
•Combo Attacks: If you manage to get both bosses to sleep, using a combination like Terra Magica followed by Comet Azur can melt through their health due to the shared health bar.
•Critical Hits: They can be staggered for critical hits, though this might be challenging. Focus on learning when they are vulnerable after their attacks.
•Patience and Observation: Learn their attack patterns. The Godskin Duo has several attacks with distinct tells. Observing and reacting to these can provide safe windows for counterattacks.
•Resource Management: Conserve your flasks and FP for when they're most needed, especially since the fight can drag on due to the resurrection mechanic.
Dodge and Positioning:
•Dodge Rolling: For the Godskin Noble's rolling attack, sometimes it's better to run away rather than trying to dodge roll through it. For the Apostle's stretch attacks, dodge rolling at the right moment is key.
•Keep Them in View: Always try to keep both bosses in your line of sight. Losing track of one can lead to unexpected attacks from behind.
Exploit Their Weaknesses:
•Resurrection Mechanic: Be aware that killing one will eventually lead to its resurrection by the other. Use this time to either deal massive damage to the remaining boss or heal/prep for when both are active again.
Conclusion
This difficult encounter requires endurance, patience, and strategy. Focus on a single boss at a time, use Spirit Ashes to manage aggro, and take advantage of the environment. Use summons efficiently, dodging and positioning, and equip gear that mitigates fire damage to avoid getting overwhelmed. Continue your journey through Crumbling Farum Azula to defeat the Godskin Duo.
