Grimrock

If you have enough herbs to brew a large number of frost bombs as well as a few speed potions and perhaps some shield then it is doable by standing right in front of the spiked gate where you enter, preventing you from being surrounded. Hasten your melee character and equip with some healing potions in the non weapon hand and top up health as necessary. This will allow you to clear the first three or so spiders and then move out into the 2x2 area to finish the rest via conventional tactics.

If you don't have a lot of herbs I would agree that you're probably in trouble!

It's a legitimate criticism of this mod however It's clear to me that when playing in hard mode it's intended for a stronger imported main game party. I try to anticipate the mindset of the mod creator when I'm playing these custom maps, They're not always nice and fair like the main game OGDA clearly likes throwing in the occasional toe to toe combat, So I try to save bombs and herbs for really tough sections that I assume will be ahead.

BTW if you think the spider ambush is too tough then you'll love the Ornate key area in the graveyard

You find the first statuette (the snail) in the western Grimforest (a bit south of the speaking stoneface which talks about: if you don't take from those who no longer need....).

There are three buttons in the southeast, it's a minor storypart.
One above water and two in the water there.

You seem to have found the iron key.
What you are missing is the riddle in the middle part of the map.
There is a lock on a pillar in the middle. A scroll in the water there and the wall text give a further hint.

You have to take out all torches there to make one light source rule over the other.

The speed potions finally tipped the scale and I was able to finish the fight. You probably also found out the bug (quite literally) that prevents the player from standing at the gate for the whole fight - a spider spawns on top the party, after which only melee attacks and fireburst have any effect as any potions thrown only affect the spider at the same grid. However, after a liberal savegame abuse to make every energy melee attack count, I was able to hack my way through the opposition.

What? You don't tank that thing from the front. ^^
Use frostbombs to freeze him, do damage, then step aside.
As an alternative stay in his back by moving while he turns and only hit his back.

In the Dwarven level where you find the axe and the shield, slimes can attack through wooden doors.
When you attack a red slime, its "blood" is still green.
The axe supposedly belongs to a Dwarven king, but its name and description are still those of Bane from LoG2.
Same for the Dwarven shield (= meteor shield).