Right, Iridion, thanks.
Not sure about Iridion 2 but some levels in Iridion 3D are not purely prerendered background loops - this level is a Mode7ish flat "floor" (the ocean) with a perspective-warping sky BG
It's not super advanced technically, maybe, but it's very well done IMO
I'm seeing a pre-rendered background loop with a little skewing applied as the player moves from one side to the other, with a lot of scaled sprites on top of it. Nicely done.
The big tell on the background loop for me is that the repeating background stuff never changes during a level.