In the opening animated sequence, Magoo's words often don't match his lips.
In the first scene with the ruby, Luanne says "Exquisite!" to which Morgan responds "Actually, it's corundum, which is an aluminum oxide." Luanne says "'Exquisite' is an adjective, not an element." Corundum isn't an element either - it's a compound.
In the chopper, Luanne has 2 money jackets in her hands. When she loose them both, we see there are 4 already in the water. However, she dropped nothing until that moment.
When the agents catch Luanne at the end, a cop takes a photo of the arrest. A little bit later, the photo displayed on the book is a different one.
In the chopper, Luanne's gun is aiming up, however she shoot down twice.
Crew or equipment visible
When Magoo is about to go after Luanne on the ironing board, someone clearly gives him a push start.
After Mr. Magoo steps off the paddle steamer, a cameraman is clearly visible in the following aerial shot on a raft under the dock.
Errors in geography
In the early helicopter scene in Brazil, the helicopter's registration number is "C-FHJJ." Canadian aircraft registration numbers start with "C-F". Brazilian aircraft registration numbers start with "P".