Just noticed that I did not write anything here!
So maybe I can add some more information bits in addition to what was already (mostly correctly) written:
The doors you can walk on instead of passing through
Early versions of R'n'D were not trying to exactly emulate the behavior of existing games, but were only (heavily) inspired by them (mainly "Emerald Mine", of course, which I played on my Amiga and wanted to have something similar on my Linux box, where no such games existed (this was around 1993/94) and UAE was still the "Unusable Amiga Emulator" (or even did not exist yet), so playing the original game on an emulated Amiga on Linux was neither an option yet).
Therefore, these doors simply were an implementation of a "door which can only be accessed with the right key" and no attempt to copy the exact behavior of the old Emerald Mine.
Later, when I tried to extend R'n'D to be able to play the classic levels of Emerald Mine, I added the door variants that come closer to the original, but kept the old ones, which were already used in user contributed R'n'D levels (and sometimes relied on that exact behavior).
The FUEL orb
The Pac Man creature (more than "it's from Pac Man!", of course
The non-sokoban lamps
As Eizzoux already wrote, they're from Mirror Magic.
And yes, these are from Dynablaster, as the name suggests.
The speed pill
That was a genuine new R'n'D game element, I think.
That's from DX-Boulderdash, a Boulderdash clone by Steffest (that's the guy behind www.emeraldmines.net
And don't forget the mole!
They're all from the game "Iceblox", a Java applet browser game by Karl Hörnell.
This is from Conway's Game of Life.
Well, sort of...
Biomaze, from what I've observed, is some odd variant on Conway, where tiles can sporadically reproduce between generations. Is this variant seen anywhere outside of RnD?
Most probably not. And "odd variant of Conway's Game of Life" more or less hits the nail on the head.
This element was the first, but failed attempt to add a "Conway's Game of Life" element to R'n'D. It contained a bug that caused the element to behave quite different from what was intended. But I found the result quite interesting and useful for R'n'D, so I kept the buggy element and gave it its own name.
What is not explained in those old messages is whether MM and its elements were entirely newly designed by Holger
No, they were not. Mirror Magic had the same intentions regarding the old C64 game "Deflektor" which I wanted to play on my Amiga in 1988 as R'n'D had regarding Emerald Mine. And, just as R'n'D, it was only later extended to be able to play the original Deflektor levels.
Later descriptions describe Mirror Magic as a 'clone of Mindbender', but since AFAICT Holger wrote both (and also AFAICT only ever wanted to use the name 'Mirror Magic', 'Mindbender' having been imposed by the publisher), it might better be characterized as an 'update' or possibly 'rewrite' of the original.
Yes, that's all right.