1. Make a sprite.
2. Set ghost effect to 100.
3. PROFIT!
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If I can think of the way that Line of Sight Works, it depends on what you want it to do.
If I wanted to add a line of sight of say, 15 degrees, I'd make a sprite which was 15 degrees, and make it as long as possible for 'infinite'. The problem is that in Scratch, it's all based on Sensors, so 'infinite' is pretty much impossible, besides using some techniques which I don't really know about. An example of line of sight is this project:
http://scratch.mit.edu/projects/Magmawulf/2314067
Hope this helps!
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