Impossible? No, just unlikely.
The nice short Santa Claus ambigram displayed to the left at first glance doesn't quite seem possible.
As you can see from the preview, you can read this as 'Santa' when the design is upright and as 'Claus' when the design is inverted.
If you wish to see the design inverted, simply move your mouse cursor over the graphic.
All items in the FlipScript store are already displaying the Santa Claus ambigram. To see them, use the menu bar at the top to navigate to an item and your Santa Claus ambigram will magically appear!