The Wanderer said
Fool can't be on the front lines? D: But he can last a whole TWO hits against a troll. Perfect, right?
I think Ares would feel more comfortable having him cover support (Moon and Vick?) where he won't be at a horrible disadvantage along with Alessia supposing she's not in the front lines. The Imagineer would probably be most effective as a wild card, surveying the field and functioning as is required. Honestly it will depend on the nature of the boss battle and how Ares can maximize role effectiveness. The Mystic Woods boss has ridiculous defense plus there will be many trolls and environmental hazards.
Fool and possibly Alessia should use ranged attacks to keep at bay anything that gets too close to Vick and Moon; Ares, Prince and Lilith should take out the trolls. Sir Valentine and the Imagineer will probably sweep.