I absolutely love this flash
Right now this ranks as my #1 favorite flash on NG.
Here is how I interpreted this flash:
Firstly it is to teach us that life is cyclical. Hence the wheels and the boy being on top of the wheel while looking at himself in the beginning and the end. Then the hooded woman represents the grim reaper. Hence the death card. 665 is the neighbor to the beast, 666. Then the monsters represent the hardships that one goes through in life. Hence why the boy was changed from a clown to a man with a mask.
I hope that I am not wrong with this interpretation.