Need help vs Lich & Pit Fiend (spoilers)

[Gherbod]

I'm playing Darkest Day, Ascension, Tactics mods

I have several times encountered Pit Fiends and they simply tear my party apart. My party makeup is a little odd and is contributing to my problem. Player is bard, NPCs are Jaheira, Cernd, Valygar, Imoen and Mazzy.

I am weak on normal magic (I do not have the "Lower Resistance" spell, nor "remove fear") I have no cleric at all (so no remove fear from there either).

Basically, my strategy is buff and rush. The Pit Fiend's fear, slow, invisibility, regeneration and gating of more Fiends is more than I can handle. I haven't managed to kill even one of these bad boys yet.

I have tried AoE damage magic... I have been able to hurt the fiend with Ice Storms... but he regens faster than he is damaged.

He slaughters my summons (elementals).

I think he is immune to ranged attacks.

Single target spells cannot be targeted because of his perpetual invisibility.

I need some advice.

- Gherbod

[Ilyich]

Get a Cleric, such as Aerie in exchange for Cernd, who is terrible. Jaheira with Ironskins and Full Plate (Level 5 spell) is an incredible tank and can fight decently well, as can Mazzy and Valygar. Then just hope for the best, Haste helps a lot too.