I recently done the giant spider in impossible with no death and a mage level 14 by using this team:
Royal Thorn and Shaman that are the base of this fight, Archmage, Polar Bears, Inquisitors. Clearly I should have used my Horsemen stack instead of polar bears because their mobility is a plus during first phase of the battle.
The tactic base is very simple, it's to occupy all free space of the board and attack the giant spider from long range:
- The first phase of the fight is to occupy asap most cases with summoned thorns even if it's a very small stack, plus few totems.
- The second phase is to replace dead thorns on border of the board (so close to giant spider) with totems that the giant spider doesn't attack.
- The last phase is just to kill the giant spider from long range.
That tactic makes this fight very easy even in impossible mode. A few teleport to solve some encumbrance problems can help do the job during first phase. During this first phase I also used once mass haste to solve some speed problem. This fight bring me about 7700 xp.