Just had a 35 round battle that went thus (I had my soverign against the spiders on a level 3 quest).
First round I kill on with fireballs, they close on me.
Second round I kill one more and injury another, they tangle web me.
Rest of battle I'm tangle webbed, they very ocassionally hit me but it doesn't matter since every time it wears off they we cast tangle web.
Result the next 33 turns I can do nothing, until the tiny ocassional amounts of damage kill me.
Tangle web needs to be resistable or have a call down longer than it's duration.