66-Boss behavior — Spawn UFOs

This is the final post of the core behaviors for this game. In this post, the boss will spawn UFOs that shoot at the player at a certain interval. The UFOs will move randomly on the screen and attack the players. A maximum of 6 UFOs will coexist; if there are less than 6 UFOs, the boss will continue to spawn new ones. When destroyed, the UFO will grant the player 50 points.