I studied judo for about 6 years in high school and college. We spent a lot of time on newaza after class. One of the "games" we would play we called "back-to-back." Two people would sit on the mat with their legs out and backs touching. A third person would call the start and you'd turn and face each other. The rules were you had to stay on your knees the whole time (so no standing up) and you had to pin or tap the person (standard judo/BJJ sort of rules applied... no punching eye pokes, etc). We kept the matches to 2 min.
To make the game more interesting sometimes we would have two-on-one. After 30 seconds a 2nd person would come in and play by the same rules... stay on the knees and help pin or tap the other person. It taught me some interesting things about how to play two people off of each other much like aikido randori and I found it to be a very valuable experience. It is not a position I would ever really want to be in but it did give a great deal of perspective.
Another game we would play based on the same rules was tossing a knife in the mix. As the two people wrestled the ref. would toss in a wooden tanto or rubber knife and then we'd play it out with that. You'd have to fight your way to the weapon and then try to attack with it. Stabs or cuts to the body, neck, etc would mean a loss. Again, not a position I would ever want to be in. Most of the weapons stuff came from the "jujutsu" classes. The "jujutsu" was an American style jujutsu based on judo kata (Goshinjutsu and Kime mostly), sport judo throws and Hakko-ryu.
We would do ground work after every regular judo and jujutsu class (four times a week) for about another hour or so. I sure was in good shape back than