Threshold

Commodore 64 version of Threshold

Threshold is a shoot 'em up style game initially published in 1981 by On-Line Systems and later by Sierra On-Line. It was available for many 8-bit computers and consoles popular during the era including Apple II, Atari Home Computers, Commodore computers, and many more. Similar to other well known shooters such as Galaxian or Phoenix, in Threshold players control a spaceship with the goal of earning as many points as possible by shooting a wide variety of attacking aliens.

As the game begins, one of the ships will launch from the right side of the screen. Once in place the ship can move horizontally along the bottom of the screen and fires upwards. Each wave of attacking aliens consists of at least a dozen, missile firing invaders which move about the top of the screen in various patterns. To complete the wave, players need to shoot all aliens while avoid the missiles they fire. When all invaders are destroyed, the game proceeds to the next, more difficult wave. There is a total of 20 different types of aliens, each with a different appearance and attack pattern. While most of the time the aliens remain above the player's ship, there are occasional kamikaze aliens that attempt to crash into the player.

Threshold adds to the concept by having a limited amount of fuel and a laser temperature indicator. Everytime a shot is fired, the laser indicator goes up slightly and slowly drops again. If players fire too rapidly, the lasers will overheat and and players will be unable to fire for a time while waiting for them to cool again. Similarly, fuel is always being used while flying; if it runs out, the ship is destroyed. This essentially places a time limit on completing the waves; fuel is only replenished when a player loses a ship and after every fourth wave when the mother ship appears for refueling. Bonus points are awarded for all of the fuel players have remaining. The final feature each ship has is a hyperdrive; this has the effect of slowing down all of the invaders for a short period of time. The hyperdrive can only be used once per ship, though. Players begin the game with five ships; a bonus ship is awarded after 50,000 points are earned and then for every additional 100,000 points.