From the Super Mario Wiki
Australia (also known as Australasia or Oceania; official name: Commonwealth of Australia) is a continent (and a country) on Earth, located in the Southern Hemisphere. It consists of the countries of Australia itself, New Zealand as well as various smaller islands in the Pacific Ocean. Australia is also the smallest of Earth's continents.
Australia has had a few references throughout the Mario series. However, most of these were in the Mario TV series. Firstly, it was mentioned on The Super Mario Bros. Super Show!, in the live-action segment, "Alligator Dundee". Alligator Dundee, an Australian man, appeared at the Mario Bros. Plumbing building, where he was hunting the mysterious sewer creature, the Ratigator.
Australia eventually appeared in an episode of The Adventures of Super Mario Bros. 3, "7 Continents for 7 Koopas". When Bowser tried to conquer the entire Real World, he ordered Cheatsy Koopa to capture Australia. Cheatsy used his Magic Wand to turn all of the humans into kangaroos, except for a Crocodile Dundee-type hunter, who was transformed into a prawn. Princess Toadstool eventually stole Cheatsy's wand, and restored everyone back to normal.
Australia also received a brief mention in the Super Mario World episode "The Yoshi Shuffle". During a football game against the Koopas, Mario was tackled by Bully Koopa, and questioned if they were playing by Australian rules. Bully responded to this remark by saying that he was going to put Mario six feet "down under".
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