When you reach your destination, which is a Nilfgaardian camp set on Marlin Coast, Avallac'h will be explaining his plan to everyone, however Ciri will not be allowed to take part in the battle. After everything is explained he will tell Geralt to prepare his potions and everything before they start - good idea so do just that while you have the chance. If you need repairs you can get them from a Nilfgaardian blacksmith.
Note: If you romanced either Triss or Yennefer, Geralt will have one more conversation with the one he chose before you head out.
The Battle Begins
Once you are ready talk to Avallac'h and let the show start. Avallac'h or rather Ciri will call Naglfar to Undvik, however Caranthir will freeze everyone and Ciri will head out to save them. You will now be controlling Ciri who will unleash her Elder Blood power and be covered in a magic aura and will literally one-shot everything, if you use her Blink ability she will wipe out everything within range. Once you reach Caranthir you will have a short battle after taking him down by around 33% HP Ciri will break the orb on his staff, however the explosion will incapacitate her, but not before she manages to escape. Fortunately Geralt will thaw out and continue the fight.
The Last General
Caranthir will pelt Geralt with magic projectiles and teleport away from him, he will also call Ice Elementals. If you start getting overwhelmed then keep your distance from him and make sure the Elementals block his view as his attacks will harm them too. Make use of Quen and/or Yrden combined with "Magic Trap" to block his attacks. And use all potions and bombs you wish. If you are worried you won't have anything left for Eredin fear not right after the fight you can meditate without any time laps to refill everything. Once Caranthir is down to around 5% a cutscene will play where Geralt will stab him and he will pull both of them underwater as a last act, so you will have to swim back to the surface.
Now meditate if you need to and head out. Fight your way toward Naglfar, along the way you may encounter Hjalmar, however this is not the time to talk so just keep pushing forward. When you reach Naglfar Eredin will be fighting or rather killing Crach an Craite, after Geralt steps in he will tell him he has something to tell him but that will have to wait for when he will be dying.
The King of The Wild Hunt
Eredin has no one to lean on anymore, however don't count him out just yet and use everything you have to put him down. When the fight starts he will goat Geralt to show him his famous "pirouette", after exchanging a few blows he will throw Geralt through a portal and they will continue their fight on a plateau. Like other Aen Elle he will teleport around the field, when he is far away he will attack with magic attacks, while in melee range he will use his sword. He is quite easy to stagger like with "Exploding Shield" once he is almost beaten he will open a portal back to Naglfar so follow him and finish him off. Once he is down to 0 HP there will be a cutscene where their swords will clash during which Eredin will strike with enough force to knock Geralt's sword back, however Geralt will use the momentum and perform a pirouette (the irony is strong) to direct it right at him and will pluck his eye out. After one last exchange Geralt will slice his throat and Eredin will tell him that they were both fooled by Avallac'h. Hounds of the Wild Hunt will now be closing in on him, however Yennefer will appear and teleport them away and the quest ends.
- Every story, even the longest epic, must end, and so this one too now nears its conclusion. Geralt and his friends had acquired the Sunstone and secured the help of Fringilla Vigo. In other words, the long and dangerous process of preparing was over at last and everything was in place for the final battle against the Wild Hunt. All that remained was to summon the Naglfar to the shores of Undvik - and straight into their trap.
- Every plan looks best on paper. It was no different this time - though every last detail had been seen to, our heroes were still in for many an unexpected danger and difficult moment. Their division of elite Nilfgaardian soldiers was frozen in ice before it could board the Naglfar. Ciri, who was supposed to stay out of the fighting, was forced into the fray to save Geralt. Meanwhile glory-seeking, fearless (or reckless, some might say) Skelligers rushed into the bay to fight both the riders of the Hunt and the Imperial Fleet at the same time.
- Despite all these complications, in the end the allies defeated the Wild Hunt and Geralt slew its king with his own hands. It was too early to rejoice, however - right before his death Eredin revealed that Avallac'h had betrayed the witcher and had his own nefarious plans for Ciri. Geralt did not know whether to trust his enemy's words - but circumstances did not allow for long and careful deliberation.
- Join Avallac'h and the sorceresses on Undvik.
- Talk to Avallac'h when you're ready to fight.
- Defeat Caranthir.
- Kill Caranthir.
- Swim to the surface.
- Board the Naglfar.
- Kill Eredin.
- Follow Eredin into the portal.
- Find Avallac'h.
- The quest Reason of State must be completed before speaking with Avallac'h, otherwise it'll fail.
- The Marlin Coast settlement is now a hive of activity with the soldiers encamped there. As a result, a few changes have occurred: one of the buildings is now fully stocked with alchemy supplies and some weapons while another has been converted into a barracks, a quartermaster is now available for crafting weapons or buying and selling goods, and the immediate region has been cleared of randomly spawning monsters.
- After the briefing, Ciri goes off for a walk. Before commencing the battle, if Geralt follows the path into the hills that starts next to where the Quartermaster is based, he can find her a little ways from the camp, practicing her magic by levitating rocks and where one can converse with her for a bit if they wish.
- If Geralt is romancing Triss or Yennefer, one of them will come to visit Geralt in the tent after Avallac'h tells Geralt to meet him at the dock.
- Speaking to Avallac'h at Marlin Coast and saying Geralt is ready to fight is a point of no return; manual saving is disabled until the epilogue.
- There's a small chance for Caranthir to freeze up for the rest of the boss battle after the player character has been swapped from Ciri to Geralt. This glitch seems to occur at random and can be undone by reloading your previous checkpoint, though if he can be damaged, the game will progress after his health is lowered to zero.