A form a passive multiplayer that displays the location of another player's death. Bloodstains can act as a warning when entering a new area.
In the Souls series, the last few seconds of the player's life are replayed when touching the bloodstain. A player's own bloodstain acts as a corpse run.
In Dark Souls, if a player does not recover a bloodstain with a large amount of Humanity, the bloodstain will spawn as a Vagrant, a rare enemy with a chance of dropping valuable loot.
In Dark Souls II, a meme developed where players intentionally die in a cave leading up to the hub section Majula. The massive amount of bloodstains in the small cave make new players think there is a trap or other difficult enemy, where there is none.
In Fire Emblem: Three Houses, resting on a bloodstain will give the character either a weapon or experience.