Vortron

Vortron is a one or two player shoot-em-up where you must protect a core from invading aliens over nine levels. The game play area is one screen and the core sits in the middle of the screen. With your ship(?) you must move around the screen shooting any aliens scrolling down the screen. The core has energy which is slowly decreasing shown by a bar at the top of the screen. You have to shoot a set number of aliens before the energy decreases fully. You can move your ship in all directions but once moving the ship doesn't stop so can easily bounce around out of control. If you touch an alien then you lose one of five lives and if playing a two player game then the next player plays. At the start you can select which level to play on.