A setting to disable screen shake. Please!
Reducing use of the mouse would reduce repetitive stress injuries. For example, on the far left side of the screen beside each troop that can currently cast, there could be a highly visible, glowing button. Just pressing the button will cast the troop, so you no longer have to press on the troop, move the mouse, and then press again to cast. Just to make it obvious to the player what’s going on: on the far right side of the screen, similar “buttons” show which enemies are able to cast. If this saves the player a second per match, then the loading screen could add a one second delay. (The buttons could be in between the troops and the gems, for even less use of the mouse.)