As of the latest update, a whole bunch of Australian animals have been added to the game. They all have one easter egg in common, and that is that when you use them in game, the landscape will change and become similar to the Australian outback. The grass will turn brown, and half of the trees will turn into brown cactus and/or twigs.
Another thing to look out for is something that gives them a slight disadvantage, performance-wise, compared to the non-Australian characters, and that is that crocodiles will be floating around in the water, in addition to logs. If you jump on a Croc, then you will lose immediately.
Other characters will have their own easter eggs in addition to the Australia stuff. For example, if you are playing as the Echidna, various swarms of ants will appear. When you approach them by moving forward, the Echidna will fork out its tongue at them.
Five more hidden secret mystery characters also exist, and each one has their own special method that is required in order to unlock them. Unlock the Drop Bear by playing as one of the Australian characters. Look for the Drop Bear to be sitting in a tree. Once you see it, approach it and it will drop on you (hence the name). Then you will be able to select it in the app store.
Three of the other hidden characters are developers of the game. One of them is the crab. The crab is a pain to get because you have to make your character go really quickly from side to side when it’s standing on the sand. This is for Australian characters only. In addition, this only works for certain Aussie characters, and you have to get somewhere around 40 points or more.
You don’t have to do the side to side hop at every single sand area that you get to, just as most of them, and just on at least one row per major sand area. It can be a little bit of a crapshoot to figure out how many of them you should do it for, but that’s part of the fun, right? Anyways, there are three more bonus characters in the game.