Maybe some television or camera? Like in Hammer (If you would implement source sdk features that would be kinda funny) where you have a camera entity with flags like how big big is the spectate angle is, etc. Then you have a special texture that is the screen.
Or like a bullet screen wall - 2 walls which simulate the shots so if you shoot on the first wall, the second wall will have a bullet flying out of it with the same angle and bullet type etc vice versa.
On this way, you could make a competitve teleportal. Because you can see the screen behind the teleporter and shoot it to hurt them.
That is my most missed feature
 
  
  CS2D
 CS2D  The Current CS2D Map Editor System
 The Current CS2D Map Editor System


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 Bowlinghead
 Bowlinghead