When the mechanical robot first appears, it has two menacing, angry looking eyebrows. Right before Ed hits it with a golf club, the eyebrows are gone.
As the kids observe Rolf beating Eddy, the bottom part of Nazz's shirt changes color.
Just before Eddy turns Ed's head to look at the "Lizard Man," (Edd) the stripe on Eddy's shirt is purple instead of red. In the next shot, the stripe is red again.