Boss Guide: Ch29-8 (Avalon le Fae Part 3)

Cernunnos fight is notorious for being one of the hardest if not outright the hardest boss fights in Fate / Grand Order, and for good reason. Not only does this fight have Story Support locked (granted the Support Altria (Caster) is quite powerful), his entire mechanics make a grindy approach nigh impossible. Furthermore, Cernunnos hits extremely hard due to his Berserker class, and hits the entire frontline with each attack. In the latter stage when he gets a boosted Critical Rate, an ill-timed teamwide critical hit will most likely end in a team wipe. The generally most effective approach against Cernunnos is to hit him hard and quick, and abuse his numerous traits and defensive weakness of a Berserker. Otherwise once the team slows down in terms of removing his Curse stacks, he will hit back with a vengeance. 

Cernunnos’s entire mechanic revolves around his Curse Layers. This is both his offense and defensive mechanism, and understanding how it works is vital to killing him for good. 

• At the start of the battle, he gets 7 stacks of Curse Layers. He gains 1 Curse Layer at the end of each turn. He also has a 30% chance to grant a Curse Layer to himself when attacking. 
• Each [Curse Layer] increase his Damage Resistance by 10% and Attack by 10%
• Each time an allied Servant attacks him, they will remove 1 Curse Layer stack and Cernunnos will recover 10,000 HP. Furthermore, doing this will also inflict a Curse Layer Pollution debuff onto all allied Servants which reduces their Max HP by 1,000 every turn and Defense by 10% for 3 turns.
• Cernunnos can inflict Curse onto all allied Servants with his skill, which he will reabsorb back to him after a turn, essentially increasing his Curse Layer stacks.
• When reaching 11 stacks of Curse Layers, he will remove his latest 3 Curse Layer stacks, and inflict Curse Layer Pollution onto all allies. 
• His Noble Phantasm, beyond being a massive teamwide nuke, also grants him Curse Layer and can inflict both Curse and Evil Curse to all allies. 

Cernunnos has a total of 4 Health Bars. Each Health Bar depleted gives him very annoying and potentially fight ending effects, while the second and third Break Bar will also recover some of his Curse Layers. Before breaking his Break Bar, Masters should plan ahead how to counteract each of his additional mechanics

First Break Bar:

• Cernunnos will inflict a Skill Seal and Noble Phantasm Seal onto all allied Servants for 1 turn. These effects cannot be removed. 
• It is very crucial to preemptively activate some defensive countermeasure to this, as having no access to Noble Phantasms and Skills for one turn can lead to a team wipe due to having no counterplay against his attacks.
• Support Altria (Caster)’s Anti-Enforcement Defense mechanics are particularly useful for this as it can take multiple hits from Cernunnos and can be used before his HP Bar is depleted. 

Second Break Bar:

• Cernunnos will gain 5 stacks of Curse Layers. Furthermore, he has a 20% increase in Critical Chance.
• The increase in critical rate makes the fight become even more RNG, making long drawn out highly risky beyond this point.

Third Break Bar:

• Cernunnos will gain 7 stacks of Curse Layers. Furthermore, Cernnunos inflict a 10% NP Gauge reduction debuff onto all enemies that lasts 10 turns and triggers every turn. 
• If the last two Break Bars were strong but not too crazy, this one is definitely over the top. Beyond this point, bursting down Cernunnos as soon as possible isn’t even a choice, but a must. 
• The NP Gauge Reduction every turn makes it particularly annoying to get Servants at NP Level 1 to get to their NP effectively without Gauge Charger effects from allies. 
• The increase in action amount is effectively a 50% increase in Damage for Cernunnos, and Masters must be particularly vigilant with Defensive Tools as he can team wipe every turn. 

Strategy:

• The most efficient approach against Cernunnos is to burst him down as soon as possible, ideally within 4-6 turns, as the further the fights drag on, the less effective a team becomes at removing his Curse Layers quickly and thus he can snowball out of control.
• When doing any Command Chain, always put the strongest attack or main damaging Noble Phantasm in the last slot of the chain. This is to take advantage of the first two attacks to remove two Curse Layers before the most damaging attack lands on Cernunnos. 
• Pay strict attention to when he is close to each Breaking stage, as he gets progressively stronger with each Bar depleted. 
• If Master opts for slower fights, having a Servant that can clear debuff from the entire team repeatedly is crucial, as his Curse Damage and HP Reduction are extremely potent if not taken care of. 
• It is highly recommended to save all 3 Command Spells before attempting this battle (this is also a good time to use the blue Leyline Stones), unless the Master is up for a more challenging fight.

• It is highly recommended to use Servants that can target Cernunnos’s multitude of traits, or at the very least has extremely high modifiers either through Critical Hits or Noble Phantasm damage. Some notable examples include Scathach (Divine), Super Orion (Demonic) or Enkidu (Threat to Humanity). Altria (Caster) can also grant her ally special damage bonus against [Threat to Humanity] trait, making her an excellent pick. 
• Foreigners are highly effective as Damage Dealers for this battle thanks to them only taking half damage from Cernunnos. Of these, the two most notable are Yang Guifei thanks to her excellent challenge quest skill set and bonus damage against Burned enemies, and Mysterious Heroine XX with her powerful modifier against enemies with [Threat to Humanity] trait. 
• Supportive Servants chosen for this battle should have good NP Gauge support for the party. This is not only useful at the start of the battle to immediately kick the Damage Dealer into high gear, but also to counter the last Break Bar mechanic. Some other useful mechanics include teamwide defensive (Dodge, Invincibility), teamwide debuff cleanse (such as Altria (Caster)) or debuff immunity (such as Asclepius).

• Note that these videos are not affiliated with GamePress, but showcase some lineups that are effective in clearing the final challenge. These can serve as a good reference for how to rotate skills during this quest or simply to have a look at the encounter before diving in.
  • Nagao Kagetora as main DPS + full Support team (4 turns)
  • Enkidu DPS (NP2) + full Support team (4 turns)
  • Chen Gong (MLB Black Grail) + 5 Support team (6 turns)
  • Robin Hood, David, Paracelsus, Mash, and 2x Altria Caster setup (10 turns)
  • Double Altria (Caster) + Assassin Li + Yang Guifei + Enkidu (10 turns)
  • F2P setup with Cu Chulainn (MLB Black Grail) as main DPS (15 turns, 1 revive)