If anyone on your team has any sort of multi-hitting spell, such as fire 2 or ice 2 (ice sword 2 won't do, can't reach the arms) then use it/them as frequently as possible. If not, start out by destroying the left arm, following the right, and finally the head. If you can get any elixirs or megalixirs, that's a bonus (megalixirs, steal from fossil ape in giant's claw -- 600 A.D.) Keep your party's health and mana up, keep attacking with the strongest physical/magical attacks that you have, and you should eventually win.