Silly thought from a total amateur:

A horror game with asynchronous online play.  

Every action taken by past players (opening a door, turning on water, breaking something, walking a path) stays in the world as "residual spirits."  

When you play, you don’t meet them directly, but you see their traces — as if explorers who died before you are still haunting the place.  

It could also be asymmetric PvP:  

- Explorers: trying to stop a ritual or uncover the truth of the entity.  

- Ritualists (name TBD): trying to complete the ritual and summon the entity.  

Each map continues until one side wins.  

When that happens, the map is reset (sealed, destroyed, or consumed by the entity).  

A new map rotates in, and players can choose again whether to be an Explorer or a Ritualist.  

During a map cycle, your role is fixed. After the reset, you get to pick again.  

Key points:  

- Solo but never alone: you play alone, but the environment is full of residual actions from past players.  

- Uncertain allies and enemies: traces might help (a door already opened) or harm (a seal already broken). You can’t tell which side left them.  

- High difficulty: no one player can solve everything. Progress comes from countless players leaving their ghosts behind.  

- Limited retries: maybe only one attempt per day. Death = your playthrough becomes another residual ghost for the next players.  

Maybe this idea is too big or too weird, but I think a game like this would be amazing to play. Just a silly thought.