The tumble effect is used to tumble 1 or more objects during an animation. To tumble an object, create your object or objects in the DETAIL editor. Still in the detail editor add an axis.
Group (not join) the AXIS to all the objects you want to tumble with the AXIS AS THE PARENT. Then load the GROUP into the STAGE/ACTION editor and add the effect as normal.
NOTE: The reason for the null object (axis) as parent is that Imagine does not TUMBLE the PARENT, just the children.