You saw a bottle on the side of a river

It looks like there is black smoke inside that bottle

As soon as you opened the mouth of the bottle, black smoke started coming out of the bottle

The smoke became a dangerous looking creature

Ryuk: Hello! You are my master from now on. you set me free. I was imprisoned in this bottle for a thousand years. My name is Ryuk. I am a demon of death. I can do anything for you!