Enemy appear / disappear script.

Hello.
Does any of you know script of appearing and disappearing enemy (or object) ?
I mean for example if someone walk, each time something appear in front of player for few seconds and disappear.
I searched forums and I couldnt find this kind of script. If I found, it wasn’t this what I was expecting.

You can set Renderer.Enabled to be either true or false to show or hide an object.

Tried. It seems to not work.
All I do is appearing 3d animated monster.