Even taking the musical talent of Celine Dion and the improvisational skills of Jimmy Fallon into account, I can absolutely not believe that they don’t practice these “Wheel of Musical Impression” bits beforehand.
Celine Dion, who appears to be having a lot of fun getting out there again, covers Cher, Sia, and Rihanna. She even gets up to do an very rudimentary approximation of Rihanna’s Work dance, which seems to make Jimmy Fallon incredibly uncomfortable.