Because of the mess they left behind (from the demolished house), the production company was barred permanently from ever filming in that part of Australia again.
Emil Chau plays an ice cream vendor, a role that he also played in Hong faan kui (1995). His appearance is meant to surprise Chinese viewers, because of his iconic status in his country.
Whole scenes from Mr. Nice Guy, were copied almost frame by frame in the Bollywood movie 'Baadshah'. Including other Hollywood movies like Rush Hour and The Mask. The results are just good fun.
In the mall cooking scene, Jackie "dices" the rolled egg very sloppily and the egg is in scraps. The next shot of Jackie throwing the egg to Miki, for a split second you can see the rolled egg chopped perfectly.
When the first Demon is thrown in the "guest house" it is obvious it is a stuntwoman. The character's hair is long and blonde, but the person thrown in has short black hair.
During Jackie's fight with Giancarlo's men at the Golden Garden construction site you can clearly see Jackie fighting Asian stunt-men instead of the guys he is supposed to be fighting.
What are the differences between the original Theatrical Version and the Extended Japanese Version?
A
As of many Jackie Chan movies, of "Mr. nice guy" too an Extended Version has been released for the Japanese market, providing a new storyline scene that enhances the character development as well as a devotement at the end of the film. unlike other Extended versions, this one has been released on DVD as well (there even exists a double DVD set containing both versions).
Of course the new scene does not make the movie significantly better but unlike earlier Extended Versions of Jackie Chan movies, this one is interesting for the international market as well since the main part of the spoken dialogue is still in English. A detailed comparison between both versions with pictures can be found here.