When Sedusa orders Blossom to stay away from Ms. Bellum (dressed up as Sedusa) who's tied to the chair, she is pointing with her right hand and has Ms. Bellum's flesh-colored skin. When the camera angle changes and Sedusa tells Blossom that she's glad the latter asked, she is pointing with her left hand and has white skin.
The kiss mark that the Mayor receives from "Ms. Bellum" (Sedusa in disguise) changes from having a glossy effect to being solid and vice-versa between shots.
According to the fax the Mayor received from Sedusa (whom later turns out to be disguised as Ms. Bellum) as Blossom reads it, it asks for $100,000,000 in non-consecutive bills, but Blossom says "$1,000,000" as she reads it out loud.
Even though "Ms. Bellum" (Sedusa in disguise) takes the afternoons off from the Mayor's office and later returns just to call the Powerpuff Girls about robberies being committed and no clues being found, wouldn't viewers be aware that "Ms. Bellum" is the real criminal before the Powerpuff Girls confirm she's actually Sedusa in disguise?