You can easily kill Walton Simons in the Ocean Lab cave. To do this, YOU MUST HAVE THE DRAGON TOOTH SWORD. This is the very powerful sword that you can pick up in Hong Kong. When you enter the cave to face Simons, quickly dart back into the passageway you came out of once he has started running toward you. Once the cutscene has ended, he will come to the door. Have the sword equipped, and be ready to strike. As soon as he runs into the door way, quickly start slashing. You will kill him VERY quickly. If you have combat strength, you will kill him instantly.