I've kicked the [censored] out of shinryu a lot of times now, and he almost never gets the chance to erase one of my characters, i've put autohaste on rikku and wakka, overdrive modes on comrade.
At the start just attack shinryu, he will counter attack and the two characters that weren't attacked charge considerably. repeat this till wakka's ready for an attack reels. After that ryu may erase one character but if rikku's autohasted he often doesn't. then use the entrust ability of iether rikku or tidus to quickly refill wakka's overdrive gauge. Shinryu has never survived a second attack reels in my game. gl <img src="/images/graemlins/laugh.gif" alt="" />
