No trolls on first four islands in my game.
Anyway, I managed to beat the spider (Impossible Skald) at level 18 with 6600 leadership. I always prioritise leadership in KB games, so I have the Valkyrie that gives leadership up to level 3 and as the leader. I wanted to try for a 'bear team' but I had a real problem purchasing anything decent in quantity. This is really annoying as I just don't have access to high level units (other than Jotuns) on these islands. Even Jarls were in fairly short supply.
Anyway, I had to go with a hodge-podge team of Jarls, Jotuns, Blue Snakes, Axe Throwers and I forget the fifth unit. Not a good mix, and Morale was not great either, but it did the job within 11 rounds. My tactic was a simple one: go for the big spider as much as possible, and whack the small stacks if I have to. I had Frenzy Level 2 which helped a bit, and Distortion 3 (which I always go for early for Mass Haste + Stone Skin, Trap etc). For the boss I just cast Mass Haste on turn 1 (which is needed for when the spider moves location) and Stone Skin thereafter. Then I just whacked the big spider for 1k-2k on a critical. Jarls seem to be really useful here. Lost about 1/3 of my troops but it wasn't too hard overall.