1) Put down the bow and use the Sword of Stone for the best speed and damage.
2) Jump straight into them and jump in swinging. You'll see your character's arm pump while you jump. When you land at the toes of the Basher you'll get about 3 immediate hits before the melee begins. This can net you between 90 - 210 points of damage right off the bat.
3) When you're at the bashers feet move your mouse left and right a bit while you hack away. Your character will appear to slide left and right with the mouse and it seems to improve your defense. You can even roll left and right without falling.
4) If you get knocked backwards you'll sometimes 'slide' back to the column and be able to resume the attack without falling. Even if you fall it's only a 5 second detour before you're back in the melee. Take a heal potion if you need to during the breather.
Take out all six bashers because it's the only thing worth while in the whole dungeon.