I was playing Heart of Fury mode recently and was making my way through the Palisade battle and the Horde Fortress and I'm sure I would have been goblin toast if I did not have the Goblin Slayer sword with me that kills goblins instantly. This sword is a complete life-saver for a few specfic screens then will be discarded. It was money very well spent.

I was wondering what other items people have found to be just as useful for one specific purpose like this?

Another example might be the Protection from Magic scroll which really only comes into its own in one specific point in the battle with Isair and Madae.

I am highly conservative so I have never played in Heart of Fury mode, however, all those items having special powers (instant effects such as death, stun etc. against specific creatures or against any creature (often with a determined chance) have obviously much greater role in HoF mode.
A good example of a very effective weapon: Hammer of Lucerne against extraplanars/undead

The problem with those items is that all of the use fortitude save, and the DC doesn't seem to be all that great. Usually, I have to hit those apoc boneguards at the gate of Severed Hand in normal quite a number of times before they get disrupted, if they get disrupted at all before dying.

Those items also have bonus damage against those specific creatures.
Boneguards should be attacked with bludgeoning weapons.

Misc weapon: Dessicated Hearts. I still don't know what it does! Oh well...
I was looking through the item editor, and it seems there is a weapon that's great versus Yuan-ti ( i think it's a longsword). Never did find it, though...

That simple flaming star +1 got me through 2 thirds of the game alone.

It can be, but you had to avoid specific creatures or destroy them using magic/summoned creatures.
There are a lot of creatures in the two third part of the game which are immune to +1 weapons.

I guess the greatsword you get from Sherincal would be very effective in the HoF mode against humans , tough I have never played in HoF.
It is very usefull in the normal game , it rocked in the rest of the ice tempel. I Hate Those Aurilites!!

Sold that sword quite early :D
Could be effective, but those Aurilities are weak anyway, they need some arrows or spells and they die.