IMO that is the version Ed Schröder participated in 1985 at the amateur championship in Amsterdam.
https://www.chessprogramming.org/WMCCC_1985
See Amateur tournament table. As hardware rebel in Amsterdam gave NO data. Because (my theory) it was this HG module they tested in 1985.
It was not commercially released (Therefore experimental). They came to the conclusion that 4 KB RAM is not enough.
In 1986 at the open championship in cologne they could participate with an accelerator card in an apple machine. Maybe 10 mhz.
And then HG gave ok for a new motherboard Rebel 5.0 that has the 5mhz and later used 32 KB Rom / 8 KB RAM.
I could repeat the amsterdam games of rebel with the rebel mystery modul.
Therefore „rebel mystery“ is more a rebel amsterdam championship version like the later rebel portorose is.
IMO one can see ed Schröder in the Amateur Championship with the participating prototype of this module in a kind of Exclusive board.
At Second 46 following he types on the keyboard of the module:
It seems to be a game against Kempelen. Kempelens screen with the move rook a8a6 can be seen and we then see similar position on the wooden experimental machine Ed Schroeder operates.
To me it looks like he has an experimental machine that is mainly an exklusive board with 1 module .
The module looks „unfinished“.
But obviously this is the reason the data in the tournament table for used hardware has no entry.
CSS only wrote :
https://www.schach-computer.info/wik...Amsterdam_1985
Quote: „ Rebel (ebenfalls NL) auf einem umgestrickten Mephisto Modular B + P“