Something like "The Most Important Movie Deaths: From A-Z" could work.

The time travelling angle is kind of cool. Every time he "dies" he gets reincarnated as the next movie death. Could be Groundhog-esgue where every day is similar, but a different death until he gets through the alphabetical order.

It could be a comic series that explores movie deaths. Could make it a bit meta/4th wall breaking by having Seth pop into the scenes and going over why it's such an important death in film.

Or similarly, you write the importance and have Seth act out the death before the description. Which is kind of what you're doing now. So once you have 26 letters here, the book would basically be complete!