Caranthir

Caranthir is the Wild Hunt’s navigator, an Aen Elle mage who guides the Hunt between worlds. He is the one who opens the paths the riders travel. In Wandering in the Dark it’s his skill that gets the Hunt through the elven ruins ahead of Geralt, leaving Nithral behind as a rearguard.

At The Battle of Kaer Morhen he leads part of the attack. Eskel struggles against him until Ciri jumps in and he pulls back. When Ciri’s power breaks loose and shatters the Hunt’s ranks, Caranthir opens a portal for the survivors and drags Eredin through it.

The final showdown comes in On Thin Ice on Undvik in the Skellige Isles. When Avallac’h and Ciri use the Sunstone to call the Naglfar, Caranthir freezes everyone in place. Ciri fights him first and smashes the orb on his staff, and the blast knocks her out. Geralt then thaws and takes over the fight. Near the end, Geralt drives his sword through Caranthir, who teleports them both deep underwater in a final attempt to drown the witcher. After he dies, Geralt goes on to face Eredin.

Combat strategy

As Ciri you only need to take a third of his health before a cutscene takes over. The real fight is Geralt’s. Caranthir keeps his distance, pelting you with magic projectiles and teleporting away regularly. Around mid-health he calls in ice elementals. You can kill them, or simply avoid them and use them as cover, since his projectiles hurt them too.

Close the distance fast whenever he lands, hit him, and be ready to chase him again. You don’t need to save potions or bombs for Eredin: you can meditate right after this fight.

Coat your sword with Elementa Oil.
Use Igni to strip his frost armor.
Throw Dimeritium Bombs at him.
Keep Quen up while you close in. Yrden with Magic Trap can also block his projectiles.
Keep the ice elementals between you and Caranthir to block his line of fire.
Have Killer Whale ready for the swim to the surface after the final cutscene.