1. He tried to avoid the battle by calling a truce. Because of a dream and several warnings from others telling him will die.
2. A Knight, without thinking, draws his sword to kill a snake (adder) and the battle ensues.
3. He tells him to throw away the sword, Excalibur, in a lake. Bedivere instead hides the sword under a tree.
4. His death and defeat in the battle. Also, he should wait for Lancelot before going into battle.
5. The adder (IN MY OPINION) represents destiny. Arthur tried to avoid his destiny by calling a truce, but the adder appears to put destiny back on track.
6. Arthur is committed to correcting the "wrong" committed by Mordred, even if he has to give his own life in the process.
7. We do not know if Arthur is alive or dead.
8. Magic is embodied in the wizard Merlin who although imprisoned in a crystal, appeared to Aurthur caused a fog to fall on the battlefield which helps Arthur by hiding his much smaller army. The sword, Excalibur, is a magic sword, the sword of power, and as long as Arthur uses it's powers for good and not evil, it enables him to do more than he could as a mere mortal.