It is a tough fight, but it can be won by figuring out how to use available resources like throwing chests full of heavy rocks for maximum weight, exploding & burning rocks, pushing enemies off the platform. Being on the platform to begin with. Taking down that double attacking teleporting pos asap, especially while still hiding unseen. And ofcourse attck from behind, use shadowhearts distraction ability for attack advantages. Sneak.. even employ poison??
And dont forget having familliars & companions present. If nothing else a lost enemy attack and at best a blinded, webbed or poisoned foe. Maybe even a final kill atleast twice something as puny as the cat has delivered the killing blow before being attacked one more time by a foe with 1hp left. And if possible have the wizard attack last, magic missile can work wonders in taking down 2 low level foes with one hit.
Still its easy compared to the bullette, full on hook horrors & wizard or the matriarch spider a aiding spider or two and 20+ baby spiders each with their own attack vs a party of 4. Fun-guy the mushy friends does help esp with zombies and if you collect all the hook horrors and bullette.. well.. might NOT want to try to oppose him. Then again duergar are relatively easy is figting them from their hut as opposed on the beach, so no need to drag the funguy there.