Joanna the Goanna is the pet of Percival C. McLeach and the secondary antagonist of The Rescuers Down Under
In the movie when Cody gets traped in one of McLeach's traps McLeach and Joanna show up thinking they've caught an animal but when McLeach sees that it's Cody he tries to blame it all on Joanna saying that she's buried a big hole in the ground. While McLeach helps Cody out of the hole Joanna spots a mouse in Cody's backpack and jumps on Cody and causes McLeach to fall in the hole.
When McLeach gets out of the hole he points his gun at Joanna, causing her to cower, but when he spots Marahute's feather in Cody's book pack he congratulates Joanna on what she's done and tries to get Cody to tell him where Marahute is but Cody rejects and runs off and Joanna chases him trapping him at the edge of Crocodile Falls. When Cody tries to get out his pocket knife to defeat Joanna with McLeach grabs him and both he and Joanna kidnap the boy and take him to their abandoned opal mines home.
At the opal mines, Joanna takes a bath while McLeach ties Cody up and tries to get him to tell him where Marahute's nest is but Cody refuses and McLeach angrily kicks his bowling pot on the fire causing some of the ashes of the fire to fall in Joanna's bath and causing Joanna to look up at her master nervously. McLeach puts Cody in a cage along with some other animals to think about telling him where Marahute is and he orders Joanna to listen if there's any disturbance from the animals or Cody.
When Cody and the animals try to get the keys to escape Joanna comes back and takes the keys away and she puts them up on the hook so Cody and the animals can't escape. The next day when McLeach goes to get some eggs for his breakfeast Joanna secretly follows him and she secretly eats all his eggs causing McLeach to get angry but just as McLeach is about to hit Joanna with the egg box he figures out that Marahute's eggs are Cody's weak spot. Then Joanna hears more noise from the animal prison room and learns that one of the animals named Frank the lizard has managed to get the keys and she starts chasing Frank, who manages to throw the keys to Cody and jumps on McLeach's gun causing the gun to go off and push Joanna into a box nearby. But just as Cody is about to free the other animals McLeach comes and both he and Joanna take the boy outside and McLeach lies to Cody saying that Marahute has been shot by another poacher and orders Cody to leave.
As Cody leaves, McLeach and Joanna secretly follow him in McLeach's truck but to their unknown Bernard, Bianca, and Jake hop onto the truck and go with the villains to follow Cody. At the nest McLeach mananges to catch both Marahute, Cody, Jake, and Bianca in the cage in the back of his truck and orders Joanna to eat Marahute's eggs so the eagle will stay rare. When Joanna sees the eggs she tries to eat them but they won't go into her mouth and feel hard so she throws them off the cliff thinking they've cracked and returns to McLeach but it's revealed that those were actually rocks and Bernard who wasn't captured by McLeach managed to hide Marahute's real eggs from Joanna.
McLeach drives his truck to Crocodile Falls and ties Cody up to the crane and prepares to feed the boy to the crocodiles but the engine goes dead and a razorback jumps out of the truck and McLeach orders Joanna to sniff around for suspicion. Joanna finds Bernard and she chases him and jumps on McLeach and Bernard manages to push them both into the water. Joanna manages to survive by swimming onto a rock and she waves goodbye to McLeach as he goes over the waterfall to his death. Presumably, she went on to live in the wild in her natural habitat.