Thank you for your quick response. I now realize it was the Ryu transformation but I already had it because I was playing on ng+.
Also thanks for the tip about the door. Funny to realise I already had the key the whole time :) Whats inside that room is also pretty nice. I expected just some chest or flames but this was even better. I can sleep peacefully now.
Again a really nice game. I also played the demo of journey of transformation already and Im looking foward to seeing the completed version of that game. Keep up the good work.