use blood lust.
create a negative scale blood lust
and
then create a positive scale blood lust.
simple as that
or you can create 1 spell that makes the unit big and small. if the spell is first used on the person, then it makes them small, if used again it makes them big.
do this by creating a trig assigned to that spell.
generic unit event, ability cast
ability being cast equals bloodlust
if unit animation size equals default unit target of ability size, then change animation size to 50% default unit target of ability animation size, else set unit target of ability to size default size of target of ability...
do you understand?