get tidus auron and rikku out, then make rikku use a Stamina Spring, ****can be stolen from yunalesca**** so your character's hp will double then swich rikku w/ yuna, make tidus use hasataga use yna 4 healing and auron and tidus can attack, use the talk command when jecht's overdrive is full, when he goes into form to unleash all of your characters and aeons overdrives also use "spare change" and release all your gil, you wont need it. then u will beat jecht.