or give everything a different type
so have
Code:
#define _type skill1
#define actors 1
#define bushes 2
#define water 3 
//etc...
then in the action for each have
Code:
action act_actor(){
	my._type = actors;
}
then everytime you need to change it call
Code:
function alpha_actors()
{
	you = ent_next(NULL);
	while(you){ 
		if(your._type == actors){
			set(you,TRANSLUCENT); // make entity invisible
		}
		you = ent_next(you); // get next entity
 	}
}


hope this helps
*code untested*