Based off the "Human I remember you're genocides" image, Remember is a self aware entity that exists in all undertale copies, only being encountered through playing a pacifist route after a genocide route along with some fun value luck. It's one goal is to make the player remember that their actions cannot be erased. They tend to possess other characters in undertale, making them directly speak to YOU, the player. Whilst being possessed the character tends to corrupt, EG sans having more detailed teeth in his talk sprite and harsh shadows on him.
They are able to manipulate the world to their command like clay on a potters wheel. They are aware of the 4th wall and will mess around with your computer (Eg changing the background of your home screen or opening new tabs on a browser). They have the ability to crash your computer without any problems. To beat them you just need to uninstall undertale or turn off your computer as they only exist in the undertale app. They cannot harm the player, only scare them.
