I managed to kill them using barrelmancy, the second time.
But yeah nasty lv 5 filled with 3 attacks a round + misty step is a very mean combo. Lost 3 out of 4 characters before being able to play my first action...
I guess this encounter will be balanced to be winnable when lv 3-4, currently unless being veeery lucky (like giths failing all their attacks) or unrealistically prepared (mirror image / mage armor on everyone + speed potions + temporary life buffs), the fight is near to impossible.
Guess Larian want to test some hard fights to know how to better balance in the future. Like the swamp fight, the hag fight, and other "end-act" bosses/mobs ; you cannot possibly win those without knowing exactly what's coming to you.
