Heres the formula to the boss: He will charge attack you after taking a certain number of steps(~7), else he will just normally attack you. He does get faster as the level progresses, but not fast enough that it will take less than 7 steps to reach you. Headshots do the most damage.

A Parting Shot 2!
+ New Bosses!
+ More Enemies!
+ Improved Graphics!
+ Improved script!

- No More Glitches!

A Parthian Shot- A military tactic employed by the Parthians who would, while mounted, feign retreat; then, turn their bodies back to shoot at the pursuing enemy.

Thus I present to you- A Parting Shot 2.