VASSAL Reference Manual

Invisible

This trait gives a Game Piece the capability to be made invisible.  Specify the key which the user will type to make the piece invisible and the name for the command that will appear in the popup menu.  The same command turns invisible piece visible again.  To the player who turned it invisible, the piece will appear transparent against a background of the specified color.  To other players it will not appear at all.   This trait actually only hides those traits that are before it in the list of traits, so it should generally be the last trait of a Game Piece. The Can be hidden by option defines who may hide this piece (and see it once hidden). Any Player means that any player may hide this piece, including observers. Any Side means that any player who has been assigned a side in a game (not an observer) can hide this piece. If the player resigns and another player takes the side, then the new player for that side will be the owner. Any of the Specified Sides allows you to enter a list of sides. Only players assigned to one of the named sides can hide the piece, but the players of all the listed sides will be able to see and modify the piece. This is useful for referee players or games with multi-player teams.

This piece sets the Property InvisibleToOthers=true when invisible.