Atari’s 1979 arcade game Asteroids has two different-sized flying-saucer enemy types.
The large saucer and small saucer are distinct UFO enemies that enter the playfield while the player’s ship destroys asteroids. The large saucer fires less accurately and is easier to hit, while the small saucer is more dangerous because it aims more precisely at the player.
The saucers add pressure to a game that otherwise centers on breaking apart drifting rocks. Large asteroids split into medium asteroids, and medium asteroids split into small asteroids, but the saucers do not follow that same fragmentation pattern. They are separate hostile objects with their own movement and shooting behavior.
Asteroids used vector graphics rather than a conventional raster display. Its wraparound playfield also lets the player leave one edge of the screen and reappear at the opposite edge, making the open space feel continuous.