On Thin Ice is the final battle against the Wild Hunt in The Witcher 3. The Sunstone has been found, Fringilla Vigo has joined the sorceresses and everything is in place. The plan is to summon the Naglfar to the shores of Undvik and spring the trap.
The plan goes wrong
Every plan looks best on paper. The sorceresses pull the ship into the world, but the Hunt strikes back hard. The elite Nilfgaardian division that was supposed to board the Naglfar is frozen in ice before it can get there, and Ciri, who was meant to stay out of the fight, is forced into it to save her friends. Geralt fights his way across the ice, through hounds and warriors of the Wild Hunt.
Caranthir and Eredin
The battle brings two long-awaited confrontations. The navigator Caranthir, who has chased Ciri across worlds, finally meets his end, and Geralt faces Eredin himself on the deck of the Naglfar in a brutal one-on-one duel. With his dying words, Eredin hints that Avallac’h has betrayed them, and when the dust settles, Ciri is gone.