Extremely Easy Yan Long clear feat. Olberic 

By bringing one of the four stars who give HP regeneration from the back row, we can ensure Olberic's survival up to the fourth turn. Olberic is equipped with Feintz's sword for extra shield shaving. Feel free to copy my setup to get this farm done once and for all.
Also, if you're worried about not having some accessories like Champion's Mark or Ritual Equipment, don't. Champion's Mark can be replaced with any accessory that gives P.Atk, and Ritual Equipment is just an awful 40 E.Atk stat stick. To be honest, I didn't spend too much time on accessories. And of course there's room for further optimization. I don't even think Fortune is needed for this to work. It's a 5-turn clear either way. The only warrior that isn't a general pool unit is Richard.
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Game: Octopath Traveler: Champions of the Continent
Octopath COTC
f2p
Yan Long Help