NOTE: Servers for Demon's Souls on PS3 were shut down on February 28, 2018. All online functionality has been removed and only imitations like default messages are available in-game anymore. All information in this article was written from the perspective of when the servers were online.
Demon's Souls supports online multiplayer through the Playstation Network, allowing players to engage in cooperative play, PvP, or trading.
Messages[]
Demon's Souls allows players to leave messages via the Select button. These messages are visible to other players online and are composed of pre-selected phrases which can be used to either help or hinder another player. Players can recommend messages, healing whoever left the message. Messages with more recommendations will appear for longer amounts of time.
Co-op[]
In Demon's Souls, players in body form may summon up to two "Blue Phantoms" by activating their summon signs. Signs are left by using a Blue Eye Stone while in soul form, and can only be left by players who are in soul form. Successfully defeating a boss will send any currently summoned Blue Phantoms to their home world, and resurrect them to body form. Blue Phantoms who help defeat a boss will not progress in the game, and must still defeat the boss for themselves.
Blue Phantoms can be sent home by using the White Eye Stone.
PvP[]
The second stone is the "Black Eye Stone", which allows the user to invade another player as a "Black Phantom", and should the invader kill the host player, the invader will regain their body form.
Emotes[]
There is no voice chat in Demon's Souls. Instead, players may communicate in-game through emotes. Holding the X button for a short time will display a list of available gestures to perform.
Item drops/trading[]
When engaging in co-op, players may give items to other player by dropping them and having the other player pick them up. A player may also receive items from other players in this manner.