The ones I don't know first:
Cosmic Epsilon, 3D world-runner, Tetrastar: not familiar with how they did it, though obviously all non-floor/gap objects are sprites in 3D world-runner.
Days of Thunder: Also unsure. Looks like the clouds are sprites, and I suspect the diagonal track is partly to have sprites on different lines, but I have no clue.
Castelian: one I want to know, since there was a TAS lately for it.
I'll add my best-guesses/observations for the rest.
Plain old horizontal scroll changes, it seems. (Bucky O'hare, red planet: 10:28 )
-plus the horizontal-lines between platforms and the parallax background, and the horizontal lines above the parallax layers…tricking your eyes into adding their own scroll values for these, despite them being static.
only the part with spikes has to be redrawn, so the updates are actually quite small.
It's still an 4-tall chunk of tiles each to draw (piston-or-blank, rivet, spike, spike). One thing is, the pistons don't all update on the same frame.
The name tables are blanked and little squares showing parts of the background are moved in software,
Attribute tables paletting things to black (or not) would make more sense to me, but not sure. It's a lot fewer updates per-frame to diddle AT…and, if I see correctly, each lighting-up shot carefully stays within one attribute-table byte's 32-px band. The level geometry then makes all platforms also align to 32px, making the shots remain threatening.
The huge beams are drawn on the background.
They don't even do the Quickman (Megaman 2) trick of having a sprite at the head of the beam to make it come out smoothly, but it's going much faster, anyway.
Of the gallery…a lot of them are just a buncha raster scroll splits, whether parallax or sinusoidal.
Metal Storm, Thunder Warrior: banking the central chasm (or other distant BG) to "slow down" its scrolling, getting apparent vertical parallax.
Crisis Force, Sword Master: combine above bank-slow with parallax scroll
Dizzy: change vertical scroll each scanline, invert scroll/compress (with per-line scrollchange) for the "Rolled" segment…and, since it looks a bit narrow, is using a thick bunch of sprites to obscure the glitches around HBlank, probably.
Boku Dracula-Kun: we've had a topic on this. Tower and (some) stars are sprites, so the moon/alien are parallaxed.
Battletoads (level 2: Wookie Hole): rewrite the tiles at the edges to slow their scroll; also note very little variation in the level BG. The color choices are handy for trcking your eyes into adding more parallax depth than exists.
Kirby's Adventure Butter Building Tower: banked tiles to look like it's spinning. The illusion doesn't look quite right on the bit where they draw three towers.
Micro Machines: the two-color distant-BG tile layer here, being 8x8 alternating squares, is very cheap to rewrite the pattern for each frame (Micro Machines uses CHR-RAM), as one will be able to write the same bytes multiple times.
Monster in my Pocket: the edges of the TV are narrow enough to be sprites, and behind the face notably shares a palette with outside it.
Rescue - the Embassy Mission: blue and brown palettes only have 3 colors, so one duplicates BG-black so it can occlude the 8x8 sprites beng moved behind it. Note that the window is only 7 tiles wide-this makes for a 1-tile(/sprite) scrollseam allowed.
Secret Ties: parallax+sprite to mix layers
Street Heroes: unconventional choiec of BG color as red, use of priority.
Summer Carnival '92 RECCA: scroll splits, scroll splits, sprite flicker, and more scroll splits. OH, hey, there's that laser effect that Minus Infinity lifted. Some manner of spritework.
Why is Taboo on there? That's just changing palette table and plain scrolling, not even having to rewrite NTs.
Final Lap: like Rad Racer, I bet: a lot of scroll splits and a surprisingly-static NT.
impossible to use ram for the graphics
nah, you can have bankswapped CHR-RAM. Only a few programs did it (inc. Videomation, RacerMate Challenge II, and Oeka Kids
), but it's possible and been done.