If you want them to become invisible after being a certain distance from the player you could do this:

Code:

---

action map_entity
        {
          while(1)
           {
             if vec_dist(my.pos,player.pos)>500//if the distance between me and the player is greater than 500
           {
              my.invisible=on;
           }
           else
           {
            my.invisible=off;
           }
           waitt(16);//only run once a second
         }
}  

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