Threshold is a typical shoot 'em up that places the player's spaceship at the bottom of the screen where he has to fend of the enemy. If the player misses an enemy and he reaches the opposite side of the screen he will reappear on the other side of the screen again. This goes on as long as the player has destroyed all enemy ships and the game progresses into the next stage with enemies approaching in a different attack pattern. Needless to say that contact with an enemy projectile or an enemy itself results in losing a life.
