I see a lot of people have pointed out that they can't progress after defeating Tengu, or that the QTE's wont work for them. I have run into a unique issue that I haven't seen anyone else mention for this boss. I tried to defeat him and ran out of potions. I left the area after losing the fight to go buy some, and upon returning, all the Tengu NPC says to me is "The trial will only be offered to those who prove their worthiness". There is no way for me to continue the quest. I tried forfeiting it to redo it, but it wont let me. I tried talking to every related NPC, no dice.

It seems to think I haven't done the quest leading into the boss fight, but because I have, and because that quest was in an instanced area that you only access once through the quest, it leaves me with no way to get back to the boss fight. Very frustrating issue, and essentially ruins the quest line.