Monochrome City Spirit Murder

In the Monochrome City it's possible to find an NPC, a girl dressed in white, that will give you the Monochrome Prayer.

Killing her will result in black chasers appearing and eventually catching you, since the exit will be blocked. Fluorette then will be teleported to a darker, monochrome version of the real world, where trying to reach the Spirit World, saving or waking up won't work, but it will be possible to leave the shrine.

The outside will look like a monochrome version of the world seen at the beginning of the game, but heading south will lead to darker and surreal areas until you will find another Fluorette with the Shovel Prayer equipped. Interacting with her will make her attack you, resulting in the protagonist being teleported to the actual real world.