If you didn't already know, you can make your chao look almost exactly like Sonic, Shadow, Knuckles, Tails, and Amy without hacking with Action Replay. Note: if there is a * next to it, that means I haven't seen what it looks like, but I'm still sure it works.
Sonic: get a spotted egg and evolve it into a neutral running type. After a few years of its life, give it even more green chaos drives and it will turn blue, like Sonic.
Shadow: get a spotted egg and evolve it into a DARK running type. After a few years of its life, give it even more green chaos drives and it will turn red, like Shadow.
Knuckles: BUY a normal red egg from the Black Market. Leave Chao World then go and get a skeleton dog and a boar. Give the skeleton dog to the chao and then give it its eggshell to put on its head, resembling Knuckle's hair. Then give it 1 and only 1 boar and it will gain its hands, which look alot like Knuckle's gloves. Note: if you give it more than 1 boar it will get its feet and tail, which will ruin its look. (evolve it into whatever you want, neutral recommended)
*Tails: Buy a yellow egg from the Black Market (you can sell the shell). Evolve it into a neutral flying type, and it will look a lot like Tails except for the wings. Later in its life, give it RED chaos drives and its ears will turn upwards, resembling Tails' ears.
*Amy- there are 2 ways that I think would make a good Amy chao. The first way is cheaper, so I will list it first.
1st way- buy a pink egg and make it put the shell on its head. Then go out and give it a few bunnies (enough so it will gain its hands and feet but not its tail). Note: this Amy chao will not have Amy's red dress, but the 2nd way will.
2nd way- this way requires you to buy a red egg (sell the shell) but have a pink shell handy. Put the pink shell on the red chao's head, resembling Amy's hair. Give it a few bunnies to cover up the hands, feet, and tail. This way the chao can have Amy's hands, feet, tail, and hair but still have the red dress. Note: evolve it into what ever you want (neutral recommended because of the dot on its head)