Imagine a game where you instantly die if you see yourself? The enemy is reflection.

— petermolydeux (@PeterMolydeux) October 22, 2012

For this one, I think the player needs to literally be Medusa. Aside from the fact that using a well-known myth reduces the need for exposition, this sets up an amazing horror story that I would really love to tell, and can really only be told through the eyes of the monster. It will be a very different species of horror, though: we can pull a jump scare the first time or two that a player gets to see themselves, blasting Medusa's dying scream through the speakers and flashing a properly horrific visage (fractal images of violence and suffering that collage into a contorted face, maybe?) onto the screen, but once the player has a grasp of their ability to control whether they see themselves or not, we need something more than the player's own reflection to scare them.

Gameplay-wise, this one must either be first-person, or it needs to be an extremely-tight over-the-shoulder view. The latter might be useful since it would widen the player's periphery (allowing them the chance to see reflective surfaces before actually seeing Medusa's face in them), but I feel like it also diminishes the effect a bit. We can also make use of the snake-hair thing as a warning device – having the snakes become more agitated as reflective surfaces get dangerously close to revealing her reflection. From the first-person, the snakes would show up on the screen edges, and might also help the player by obstructing the periphery (to help avoid accidental glances).

Any other entities Medusa encounters in the game have to turn to stone the moment they cross in front of the player's view. The ability to create instant, line-of-sight-blocking statues has me thinking about navigating mirror mazes, but such challenges would be mostly for changes of pace from the game's real focus: Medusa's search for a place of comfort, safety, and, most problematically, community. Throughout, Medusa will interact with other characters, sometimes trying to befriend them, other times (accidentally?) killing them. This would, given her condition, frequently be via speech and sound alone, so one might want to make sure that whatever system governs those conversations is appropriately deep, even if it just means extensive dialogue trees.

This is a game about loneliness, abandonment, futility and existential crisis. Medusa doesn't necessarily hate the other humans she encounters, but they nevertheless fear her and shun her, and they ultimately die as soon as she encounters them in person, leaving her alone and bereft of a meaningful life. Medusa is a modern symbol for nihilism: she represents the horrible "truth" that we don't want to acknowledge (that life is meaningless and the world is uncaring), because proverbially looking that truth in the eye feels, to us, like death. That's why, after overcoming the challenges of the game, players should find themselves utterly alone in the game world, their efforts ultimately without reward, and with nothing left to do but look into a mirror and end the game.