Thanks for palying!
You opened my childhood memories, I remember that I also played Nosferatu (but during the jam I completely forgot about this game).
The secret ending is revealed if you collect all the ducks, but it is made for fun and is not necessary. So you haven't lost anything. But what if the second duck is in the place where the enemy runs out. You can manage to exorcism him, but I won’t tell you exactly how :P