Hi,
actually, it's way easier and everything is there to do that without the need for custom actions.
I have attached a sample, where as you click, the cube will move towards the mouse point.
The set up is very simple, one object is following the mouse using the action "mouse follow", then the cube is using the "move towards" action to move towards this target if the mouse left button is down.
notes:
-- check the way the camera is setup, it's important. The z distance is the same as the mouse follow setup so that everything stays in the same 3d plane
-- the move toward action has its Finish distance set to 0 so that it never stops catching up even if at some point it's perfectly positionned where the target is.
If you have questions let me know.
Bye,
Jean