The MMV gained 70 ELO over its predecessor but made a name for itself as tactical monster because it often could solve deep combinations strewing with mates in 7 or 8 moves while only doing 500-600 nodes a second on a 5 Mhz 6502 processor.
That's was quite new in those early days.
The system is described at the Inside REBEL page, paragraph long checks.
A couple of examples, again the German WIKI is quite helpful.