Lol, take it from a dude whose main username is White Shadow, and loves riddles
The answer is Shadow
It only appears where there is light, but if light has direct contact with it, such as a flashlight beam, it'll fade.
The letters are A, C, E, and G. you can remember this by the acronym ‘All Cars Eat Gas’
Answer:
tempos
Explanation:
Composers change the key to create different tempos. I think so