How could I get the mousepointer to look like a crosshair?
Make a crosshair that doesnt move or touch anything and make its behavior “MouseMove with its y and x connected to y and x of Position”
yeah but you will still see the mouse
Then im not sure 
there isnt really a way to do this besides put an actual new behavior into the game and for that you would need to be the owner of the website sorry but this is only as far as i know