How do I make a BillBoard Gui only visible to some people?

Adorning it to a brick will let everyone see it. If the persons on a certain team and you want only that team to see it, you can run a if statement

--reference the player
if player.TeamColor == BrickColor.new "Brick color here" then
(GUI).Adornee = Brick

I haven't tried Adorning it to the players GUI. That might work.

Oh, just remembered there's a "PlayersToHideFrom" Property for BBGUI's try experimenting with that.

Adornee it to the person's PlayerGui.

Or put the BBGUI in to the Player's PlayerGui and Adornee it to the brick. -- I don't know if that works, someone correct me, if it doesn't.