I failed mines today too, made 1 major mistake and that was using a skill that reduces rage meter when it wasn't in rage, could have avoided a 2nd overdrive by getting her into stun but ended up taking 2 ragng overdrives and wiping my main party leaving my 2 subs to die at it at about 10~15% hp. If I had Sol, I probably would be able to do this as I'm using Amaterasu with my light party and she's not really providing much, especially in the damage department. Still haven't really figured out the best cross skill for Mordred for this fight and thinking I might use Joan instead but I'm so reliant on dizzy I'm not sure if it's worth the change.