Use Movie Fixed (also called Start moving in a direction) to start the instance moving in a particular direction. You can indicate the direction using the buttons with the arrows on it (the directions are 0,45,90,135,180,225,270 and 315 degrees). Use the middle button to stop the motion. Also you need to specify the speed of the motion. This speed is given in pixels per step. The default value is 8. Preferably don't use negative speeds. You can specify multiple directions. In this case a random choice is made. In this way you can let a monster start moving either left or right.