Toribash
Improvement. Playing a bit of single player every so often will also help. It help you put the skills you learn in multiplayer together to make your game plan. If you have the time play in the ufc octogon for 1000 frames 10 frames per turn 30frame dq. Alternate between tori and uke. Teaches you fine control of your tori. And the types of attacks that end a stable top control. Also look for inspiration from real world martials.
Depends on how diamond plays. I can give yu a better answer if you can describe the play style. With the information at my disposal i would say using solid fundimentals. Ask your self. Am i stable?Are they stable? Am i set up for an attack? Will this attack end with me in top control or a safety position? Work your way though these questions if its a no. Make it a yes. This will help keep you alive long enough for them to mess up enough for you to capitalise on.