Mirror Image

How do i detect the units made by mirror image and make them do stuff?

It's just a unit so the orders are no different.

Units created by mirror image do not set GetLastCreatedUnit().

Use the EVENT_UNIT_SUMMONED event to detect when a unit is summoned, then check that the summoning unit is of type (whatever your caster is) and that IsUnitIllusion(GetSummonedUnit()) == true.
That will give you the images you need.

or you create a trigger with "Unit Enter Region Event" and check if this unit got needed ability ID (the buff of mirror image) or check IsUnitIllusion(GetTriggerUnit()) == true