Is there any way to make mules drop atm i press hotkey (w/o leftclick?)
Within the Hotkey section inside Global -> Unit Management there is an obscure option called Choose Ability or A.I. Target, adding an secondary hotkey option (strongly recommended) will let you use keyboard buttons to cast an ability along with left mouse click.
If you set this to the same as the ability youre using you can rapidly cast spells, for instance having MULE and the Choose Ability or A.I. Target option both to E will make you rapidly cast the spell without having to lift the finger.