Are the objects that you downloaded to the World not moving as intended, or do they keep getting flattened?
Then try modifying the [Physics] values, or try the [Align] function.
You can use the functions in the following situations.
1. Physics function: select the object, and turn the [Physics] property to [On] to change the gravity and mass. Uncheck the gravity, and toggle with the mass value to make the object move or fly. If you check the gravity and increase the mass, the object will not move easily.
2. Align function: if the object is not moving in the direction that you want, check the [Align] function at the top! The [Align] function will arrange the object at regular intervals, and you will be able to modify the move-rotate scale.
To learn more about the Physics function, check out the link below!