
The most extended common RPS game I know has 5 elements:
ROCK --> SCISSORS --> MATCH --> PAPER --> FOUNTAIN
where each element defeats the next two in the line - which is in fact a circle - and loses to the other two:
ROCK...
...crushes/ immune to SCISSORS
...crushes MATCH
SCISSORS...
...cut MATCH
...cut PAPER
MATCH...
...burns PAPER
...lightens FOUNTAIN
PAPER
...covers FOUNTAIN
...wraps up ROCK
FOUNTAIN...
...swallows ROCK
...swallows SCISSORS.
BTW, there's also a guy who published an extension with no less than 101 elements on the internet! He even invented plausible handsigns for each of those 101 elements, though both hands are needed for most of them. It was quite funny to read that and email around with him a bit, I even purposed to him an extension to 103 elements which he found quite interesting


Now I thought about an RPS game with BD elements. My first result has 5 elements where I think the outcomes are quite intuitive and logical:
ROCKFORD --> DIAMOND --> DIRT --> BOULDER --> FIREFLY
ROCKFORD...
...collects DIAMOND
...digs DIRT
DIAMOND...
...outvalues DIRT
...outvalues BOULDER
DIRT...
...carries BOULDER
...blocks FIREFLY
BOULDER...
...kills FIREFLY
...kills/blocks ROCKFORD
FIREFLY...
...kills ROCKFORD
...guards DIAMOND
This looks quite extendable, as such classical elements like amoeba, wall, mwall, slime... aren't in it yet.