We had PET computers in my high school, 4032's IIRC, and a few classic games to go with them - the excellent Space Invaders port, Star Trek of course, and a few others. These all used PETASCII for graphics, if any.
In my last year there I found someone had brought in a bunch of new games, and one in particular still strikes me as odd to this day. It was a shoot-up-from-the-bottom game like Space Invaders, but had several submodes, in the fashion of Gorf or Astro Blaster. I seem to recall that the player's ship was two triangles and perhaps fired two shots at the same time?
All of these sub-games featured graphics that were far in advance of what I had seen before. One in particular consisted of a small number of alien ships (two?) mid-screen shooting lighting bolts down the screen. These were not typical graphics, they appeared semi-transparent and seemed to be vectors. Beyond that, everything was fast.
Can anyone hazard a guess what this game may have been?