It's been a while since I played BaK but I think applying flame root oil to your armor before combat makes you immune to cold based effects including fetters of rime.

The description mentions neutralising the cold effect on blades, but I hadn't thought of using it against Fetters of Rime. I've finished the game now. It turns out that the group of lizard-wizards outside Malac's Cross was the last difficult combat in the game. The last two chapters were laughably easy, even with somewhat underdeveloped characters. Still, thanks for the help!

My preference for dealing with those multi-caster battles was to ensure that the characters had summoning items handy. In particular, there's a horn that summons a pair of war dogs, which when dropped in the middle of the caster pack will not only disrupt their casting but provide alternative targets. As long as the PC caster doesn't get paralyzed or killed, you can keep throwing out new summons every turn and clutter the battlefield enough to keep the enemies from getting anything off.

This can also be helpful in Chapters 5 and 7 since the game usually starts Patrus off in a stupid location (ahead of and apart from the other two), ensuring that he gets mobbed right off the bat.

There is also a spell available in Chapter 6 (albeit in a different area of the map) that has the potential to kill off every opponent as long as Owyn acts first and has enough health to sustain it: Mad God's Rage. Only usable outdoors, but if nothing else works, it usually will.

I think most people have a problem here because when you start Chapter 1 your inclination is to head strait South to Krondor.

However, you need to head North first and complete lots of exploration and side quests (that will raise your skill level) long before you ever head down to Krondor!