function bypassSoundPlay()
{
    snd_play(SND_FINAL, 100, 0);
}

if((mouse_left==1)&(my.skill6==0))
{
    on_mouse_left = bypassSoundPlay;
}
else
{
    on_mouse_left = NULL;
}

if(mouse_left)
{
    snd_play(SND_FINAL, 100, 0);
    while(mouse_left) wait(1);
}

function event_blahblah()
{
	var snd_once = 1; // ******
	while(1)
	{
		my.alpha = 70;
		pick_function();
		scan_you();
		// play sound only if skill6 is "0" and snd_once is "1":
		if(my.skill6 == 0 && snd_once) // ******
		{
			snd_play(SND_FINAL, 100, 0);
			snd_once = 0; // don't allow to play again
		}
		// till we release mouse_left:
		if(!mouse_left && snd_once == 0){snd_once = 1;} // ******
		wait(1);
	}
}