Revision dafc438a-0c94-4e0c-99e8-d4faa7ded83a - Code Golf Stack Exchange

# [C (gcc)], 142 bytes

<!-- language-all: lang-c -->

 #define r rand()
 m;b;q(){m=r;m&30||q();}f(){q();for(b=(r%4+1)*5;--b;)printf(b%5?m&1<<b%5?"%c%c":"--":(":"+!q()),"RWSC"[r%4],"urgbypcw"[r%8]);}

[Try it online!][TIO-kss19rcm]

[C (gcc)]: https://gcc.gnu.org/
[TIO-kss19rcm]: https://tio.run/##HY5RC4IwAITf/RVroWzpQCkhnNJD/6Aeeggf3HQyaMumIaH@9dbs6e4@OO44aTm3dls3QuoGGGAqXSPsKcroC@FJFYaqYB/Ps0t0EQ6tRjwNYgUy/iFM8C6lhDCKOyP1IBDz05MKkjxfDfS5z2EGCYEZchpuXB1H8HK7nuHd9csIvk3LPh0f13ws3YpVldQIg8kDoP8fGqRqUIwxdcR9oN5iv1w8qra3ZPwB "C (gcc) – Try It Online"