when Rikku is doin her thing with the sphere grid, she moves past a level 3 or 4 lock blocking holy, I left her there until i got the appropriate key sphere then used a wht magic sphere to make yuna learn holy. Then i made sure my party consisted of three fastest characters: Tidus, Rikku and Yuna. Rikku should be your healer, holy waterer, yuna should cast holy every turn (have planty of ethers!!!) and Tidus should cast hastega when needed and attack. Make sure that when ur done with part two everyone is zombied or megadeath will kill you. Hope this helps, I still thought it was hard as hell.