1) The explosions are glitching for me - rather than use the spin-jump stars, they're using a foot tile I don't recognise offhand - https://somebodydptest.files.wordpress.com/2019/02/glitchedbombkoopasplosion.png - What do I need to edit to fix that?
2) What would be needed to make the koopas stay in their shells when jumped on? (I have SMB3 Koopa Patch v2.0 installed, so I probably just need an indicator of what numbers to insert there...)
Works fine for the most part. I only have disabled the "don't disable clipping..."-thing for the shellless Koopa which had the glitch that the Koopa behaved weirdly (also affecting the alternating height jumping Para-Koopa).
The Koopa also behaves like a normal shell when eaten by Yoshi so keep that in mind when creating levels with it.
The Koopas also are invinsible to fireballs but not to capes. You can fix that if you do the hex edit mention in the ROM Map for $02A0B9.