River Devil

The River Devil is a black, tree-like creature that blocks the single north-south road of Eastern Hyrule in The Adventure of Link. Though citizens of Nabooru speak of him in fear, he does not attack, and serves merely as an obstruction. The only way to pass him is to play the Flute found in the Palace on the Sea.

Trivia

 * The River Devil has a much more mammalian appearance in the Japanese FDS version, being bipedal and having brown skin. On top of that, it was simply known as "the monster." It is unclear as to why this was changed.