After adopting the Carrousel complication over Tourbillon, Blancpain attempted to explain the differences between mechanics of the two, but their written explanation was too complicated even for the experts to grasp. Now, they have released a video comparing the two.
Before moving on to the differences, let us understand the similarities. Both mechanisms use very similar methods to compensate for gravity through balance wheel. Balance wheel ensures accurate timekeeping. Moreover, each of these mechanisms is very similarly constructed and the difference is not apparent.

Each mechanism has a very similar looking energy accumulator, counting transmission, and distribution. However, the Carrousel system has an extra wheel, called the intermediate gear train that transfers energy to the time display – and this is the most significant difference between Tourbillon and Carrousel complications.

The Karussel Blancpain
It is not necessary to understand any of the above to appreciate the beauty of a mechanical watch. Just watch this video and be amazed.