In the shot of Mario and Luigi fighting and Toad tells them to "chill out," the wall can be partially seen below the left corner of princess. Therefore, the princess looks like she's on the wall and not the floor.
When Kooky is reeling Mario in through the warp pipe, there's a shot where Kooky's face is the same color as his skin instead of green.
When Kooky is telling Luigi that Mario has been turned into a slave, Kooky's face is the same color as his skin instead of green.
When Luigi shakes Mario after being restored to his old self and asks if he's alright, Mario's hair turns black as he's being shaken. Then his hair is back to brown.
As Mario starts to insist that the argument was his fault, his hair changes from brown to black. In the next shot it's back to brown.