The majority of enemies are other spaceships, all of which must be destroyed before a level is completed. They appear either from the center of the screen or from one of the edges, and move in swirling patterns. They can shoot the player's ship or destroy it by contact. They hover near the center of the screen after completing their deployment pattern, and occasionally fly outwards and shoot at the player. If they are not destroyed by the player, the enemy ships gradually fly away one by one.
There are also several other types of enemies: satellites, asteroids, and laser beam generators. These appear intermittently and soon disappear of their own accord if not destroyed by the player.
Fighters
Fighters are the common enemy. At the start of the stage, they will normally arrive in four groups of ten. They are worth 100 points each (unless they are in holding, where they are worth 50). If you kill an entire wave during deployment, you receive 1,000 points, plus 500 points per each wave killed in that stage.
Space stations
After all of the fighters have been deployed, space stations will appear between you and the center formation after a number of enemies have been destroyed. Depending on whether the player has upgraded weapons, the middle object may be a third station (shown left), or it may be an weapon pod (shown right).
The weapon pod appears if the player still has the original single gun. When shot, the pod releases two bursts of energy which travel in opposite directions around the screen. Once both bursts have hit the player, the player's weapons will be upgraded to double shots.
Whether three stations appear, or two stations and a weapon pod, the objects gyrate in small circles while shooting at the player. Destroying these objects can be tricky since they are situated much closer to the player than typical fighters, so their shots do not have as far to travel in order to hit you. You earn 1,000 points for the first station destroyed, 1,500 points for the second, and 2,000 for a third. The orb is worth 500 points.
Asteroids
First appearing on stage 2, Asteroids fly straight outwards from the center of the screen at regular intervals. The trajectory they fly on isn't always aimed directly at your ship; they tend to fly a little bit to the right or left of your ship, depending on which was it has been traveling. It's possible to avoid taking damage if you hold still, but this may put you in further danger if enemy ships are shooting at you. Asteroids cannot be destroyed, but a small point bonus is given for shooting at them.
Satellites
Satellites occasionally appear from the center of the formation, and fly out to the edge of the screen. As they fly, they bounce a high-energy signal back and forth between them. Getting caught in that signal will destroy your ship, as will colliding with either satellite. Destroying either of the satellites deactivates the beam. They are worth 200 points.