Demon Protocol · published
Rotating planet backdrops. Each wave band now hangs a slowly-rotating, lit planet in the upper-right of the play field.
Waves 1–5 — Earth
Waves 6–10 — Mars
Waves 11–15 — Saturn
Waves 16–20 — Toxic
Waves 21–25 — Hell
Orbiting moons. Each world has one or two moons on tilted elliptical orbits that pass in front of and behind the globe, with correct occlusion. The ringed world's rings also pass in front of and behind it.
Boss-wave surface. Boss waves swap the planet for a Moon-Patrol-style scrolling planetary surface: jagged far mountains, a mid-ridge, cratered foreground ground, all in parallax along the bottom of the screen.