The clues are starting to explain themselves

The black feathers led me to a ruined shelter hidden deep within the Forbidden Forest. I expected another doorway, another riddle, or perhaps another creature waiting to kill me. Instead, I found a book. Most of its pages were blank. Others changed whenever I looked away. The only chapter that remained the same was already open when I arrived. It spoke of two phoenixes born from the same cycle: one of flame and one of shadow. At first I thought it was just a story. Then I noticed the sketch of my wand in the margin. And for the first time since entering the forest, I stopped hoping these were all coincidences.