OK this is getting frustrating to me too. I created a empty test level and added:

code:

synonym syn_male_fire_mutant {type entity;}

function male_fire_mutant
{syn_male_fire_mutant = ME;
}

/// functions to spawn the mutant models
function spawn_male_fire
{
temp.x=35;
temp.y=355;
temp.z=275;
vec_for_screen(temp,camera);
create(<guard.mdl>,temp,male_fire_mutant);

}

FUNCTION remove_male_fire () {
//REMOVE syn_male_fire_mutant//this works too
syn_male_fire_mutant.INVISIBLE = ON;

}

ON_1 spawn_male_fire;
ON_2 remove_male_fire;


This works with turning the entity's invisible on or by removing it. This is of course just by hitting the keys and you must be calling it from another function. Refresh me on how you are trying to acheive the on and off functions.