Divinity: Original Sin Enhanced Edition

Boss King Boreas. Tactics on Valiant.
After talking with Boreas, Bairdottir uses the “Stealing Will” and then “Draining the Soul” scrolls on him. Next: the rest of the characters surround Boreas. Important! To avoid slipping on the ice, use Divine Light in this area to melt the ice along your feet. On the same turn, use the Inspire skill and then Crippling Strike on Boreas. Because he is invulnerable to Knockdown. Also use the Poison Dart scroll, because Boreas is vulnerable to poison. And of course hit him.
On his second turn, Boreas will summon an Ice Elemental and surround himself with ice particles. On the ice elemental, use the Exorcism scroll. You destroy ice particles using the "Twister" skill. But at the same time, so that you also capture Boreas. In addition, on this turn, call Nick. And when it’s his turn to make a move, use his skill to cast “Disease” on Boreas. The remaining characters use the "Twister" skill to get all the ice particles and Boreas with them. Use Madora's Flurry of Blows skill. During these two turns you must remove Boreas, at least two-thirds of her life.
On the third turn, the "Drain Will" and "Soul Drain" scrolls will cease to have effect, but "Disease" will continue to operate. Use the silver arrow to lower Boreas' armor. And after that finish him off. That's all.
I destroyed Boreas in the first phase. And this can really be done. But remember the main rule: Never let your characters slip! And not one of them should go through the “Freeze”!
Attention! This hint is written in the context of the "Please Don't Die" trophy. To understand what we are talking about, look at this trophy.

If you defeat Boreas in Hiberheim, he will drop a staff that will immediately start talking. The staff must be taken to the forge in the Lava Fields in Hiberheim and combined with the large lava thing >____< Elements released - the trophy is yours.