Here's a copy of my post in the Introduction sub-forum:
Stumbled upon Elimination today, thought nobody was going to use the Gemini source code. Glad so see somebody decided life wasn't gonna get any better
I haven't touched z80 since Gemini, the first TI83 infinite plane demo (I see there's a Zero-Wing thing going on, goodie) and some hopeless excursions in 6 DOF 3D culling. Still, would be glad to help if there are any questions about the Gemini code. Tried to post in that sub-topic, but wasn't allowed to so I'll just copy-paste my post here.
Few things about me for those who haven't met me (I do not recognize many of the nicks around here): I'm cynical, glad to offer constructive criticism but I hardly ever pat people on the back unless they're about to pass. So let me get this over with: Looks nice. From now on I'll run in cold mode.
Skimmed through some topics, I do agree that far away sprites look a bit blocky compared even to the ancient Gemini. Remember to design levels taking into account the crappy resolution of the TI84, long distance encounters need some space. I hardly ever did, in fact I never even played through map 3 in Gemini IIRC, but I figured after I had released the game. Turned out alright.
It seems you have a way to store loads more data on the calc than Gemini ever did, so I would suggest mipmapping for all sprites. Use pixel-wide details, select a mipmap by the projected screen size and only ever scale up, never down except maybe beyond the smallest mipmap. If you go for 32x32, 16x16, 8x8, the scaling-code should be fairly trivial to update.
The perspective projection looks very harsh now that you have the caster fullscreen, I would suggest generating new perspective LUTs to get larger walls for a longer distance. I don't remember if I used "f * x / z" of "f * x / (z + z0)" with z0 being a hand-adjusted parameter. Try the latter option and play around with z0 to get a "beefier" perspective projection.
The gun perspective looks odd in fullscreen. Don't settle for a Doom approach, they did that back in '93, just do it right.
I remember there was a bug with the hit detection in Gemini, which was the bug that was mentioned in the dev docs in the Gemini zip. Did anybody find this and fix it?
Personally I think the background esp. on level 17 looks terrible Devil Your decision entirely and if people want it, by all means go for it. I seriously thought you had introduced a bug in the graphics code when I saw that vid on yt...
I may not be super-responsive, but ask questions or whatever and I'll try to answer them in due time. Try PMs if I go silent.