Q: Which Boss is affected?
A: The Tengu-Bossfight from the [Mushroom Shrine Tales]-Quesline
Q: What disables a proper process to end the Boss fight successfully?
A: From two attacks Tengu is supposed emit a purple "Magnus-Aura" (after flying from the background before landing AND before the stompattack), which is interactable via the spacebar to initiate a sequence after which the Boss recieves damage and in consequence can be defeated. BUT, these purple AOE won't show up under ANY circumstance so the bossfight becomes impossible, the only way to damage the Boss is via said sequence.
Was played via Nexon Global Launcher.
Unsuccesfull workarrounds:
-End Client and restarting game
-Relogging into the game
-Leaving and reenter entrymap and bossfight
-Dieing and reviving
-Waiting for prolonged time
Tl;DR: Bossfight Tengu impossible, purple aura at miss, mechanics to beat Boss can't be done.