To quote from the discourse blog…
Narrative Welcome Bot
Perhaps the biggest new feature in this release is our narrative welcome bot, which greets new users with a personal message and offers to interactively “play” the Discourse game with them
https://clarionhub.com/uploads/default/original/1X/3247b5a0d5d2aa3269fd00a452accc99c851a6d0.mp4
As an existing user you can kick start the @discobot just for fun by sending a message to it.