You speak of a Form containing controls. So let's assume you're using Windows Forms.
MouseUp fires whenever a mouse button is released. From what you tell us, you want to use the MouseHover event instead.
Normally, you would have to create a method that takes a control as an argument and make it output the control's name. Then you would subscribe that method to every control's MouseHover event.
Or maybe a
global mouse hook[
^] is what you're looking for.