They reveal on day 1 and ask everybody to pm him their roles whilst also asking the doc to heal them.Note this is only possible on setups where the mayor can be healed (which is the wrong option in my book but whatever)
Point is the troll mayor is taking heals that could be provided to the investigator sheriff or jailor not just night one but the entire game.It ruins all mystery as to who the mayor is, please make the mayor unable to be healed in your setups guys!