ha lol, that was kinda confusing me, but do you mean on the minimap or on the screen? but anyway, i guess you want only some units to be visible, so you can try playing around with the "Soulstone" item from the campaign, as it does make your hero visible in fog of war when you caught another hero with it (use a dummy hero maybe). or another solution which might work, you put a building with some weird classification somewhere, and make it almost invisible (very small, colors, etc.) and place it in an area which is visible to everyone, give all those units a phoenixfire ability with unlimited range and no damage and which can only attack this building classification, normally attacking units get visible in fog of war, and if phoenixfire cooldown is sth like 0.01 you will always see the unit, although i don't know if this attack sight thing works for phoenixfire