Robson Moura is a name that doesn't need much explanation. He is 7x World Champ and 8x Brazilian Champ. To say hes jiu jitsu is top notch or world class is an understatement. I know from experience that you can literally ask him about any position, regardless of grips and hooks, and he will immediately respond with a detailed and thorough explanation of every sweep, counter, and submission from there. He's like a 5'7 jiu jitsu encyclopedia of amazingness.
Check out this sweet vid of Robson working from a modified half guard to an armdrag. Do we even need to suggest you write it down and try it tonight at the gym?