Sorry to hear you're having trouble with it, you're supposed to follow Willow (The Blue Flame) during the fight that's why she tells you to stay close before the battle. Which attack Cerberus does is randomized but if you follow Willow and stay close to her you will win the fight a majority of the time. The only attack I will say requires a bit of reaction time and is somewhat annoying is the one where she runs directly forward otherwise I think the fight is pretty balanced, I'm glad you like the rest of the game though! :D