Advertise this setup as either closed or something super standard such as (9x VT, 2x mafia Goons, 1x Mafia Roleblocker, 1x Cop, 1x Bodyguard)
When the game begins include rules typical for this standard setup. The players know that they are VT, but believe there are the stated number of mafia in the game.
However, unbeknown to all the players, the setup would
13x Vanilla Town Players.
The players that wins are the players that makes it to Lylo/Mylo, however, they believe that the win condition is to remove all the mafia (which don't exist).
The game will make an excellent long term april fools prank and increase net frustration levels.
April fools is in a few weeks. Think that sign ups should kick off on April 1st, or the game begins April 1st.