My Meaning
I believe that the boy is depressed. He is afraid of the world and hides behinds his mask. The key will release the mask when he is ready to face the world. The 665 (step before hell) card could be near death which is not and he is thinking about suicide. Which then would be 666 because in many religions suicide leads to hell. When the spider thing grabs him it takes him to the outside world or school you see what his world is like for him. He is small and caged. He is bully and teased by the "monsters" which might be his peers or just other civilans. The monsters make him into a clown, embarrass him. He then enters a blimp which offers him cards and blindly he picks one. The boy blindly chooses his fate as if a coin toss. He then goes back to the world or school and gets a key from the spider which I believe symbolizes his choice to face and conquer his fears.
I do hope the artist is not making this film based on his experiences. Do continue your work despite what others think. For every one who is uninspired, you inspire a million more.