Three tricks to beating the end:
1. Constantly send hobbits at him. They die of course, but he has to stop to kill them, so he approaches a little slower, so you can hit him with more arrows.
2. Make sure you have all of the defense upgrades (shield, trap, turret)
3. Fire arrows constantly by holding down each button, then clicking outside the game or the browser.
 "Epic war"){kind=icon}
 "Arachnophilia"){kind=icon}
 "Drone Wars"){kind=icon}