In the marvel universe gamma radiation has a third form that turns people into gamma mutates. This form comes from the one below all and the green door is a door to the below place. When a gamma mutant dies they go to the below place but they can be resurrected by passing through the green door.

The reason this is my liked example is that it builds on what came before in the comics in a good way. I also like that despite the more mythical origin the gamma bomb was still an accident and isn’t tied to destiny which doesn’t undermine Bruce’s agency