Your Chao will gradually change over time as it ages. After it evolves, the Chao age has a much more pronounced effect on it’s appearance as it grows older. At first, you will find it very difficult to tell what ability type(s) the Chao has. Depending on the animals and Chaos Drives that it interacts with, you will start to see all sorts of appearance changes in your Chao!
As previously mentioned, a Chao is considered to be a child for the first few hours of its life. It then forms a cocoon and evolves when it is ready.
As your Chao edges closer to evolution, you will see its body shape and colour (if it is a regular coloured Chao) change towards what it wants to evolve into. You can see this change for yourself using the Chao Island 3D Chao Viewer. A Chao will evolve into the alignment and ability type that it favours most at the very point it enters its cocoon.
Along with the Chao’s alignment being Hero, Dark, or Neutral, it also evolves into one of five different ability types. These ability types are Swim, Fly, Run, Power, and Normal.
After evolution, the Chao will start to morph again as it grows older based on new animals and Chaos Drives you give to it. This way you can create all sorts of combinations of Chao, such as a “Neutral/Run/Fly Chao” which is known as the Elf Chao. For a full gallery of these Chao, check out the Chao Gallery!
The Chao’s appearance after it’s evolution is not permanent, has nothing to do with stats, and does not take place at any specific age (the changes gradually get more distinctive as the Chao gets older). You can always change the second evolution of a Chao by simply giving it different animals or Chaos Drives. For example, if you have a Run/Fly Chao, you can give it Power animals and it will change into a Run/Power Chao as you continue to give it more. The changes are determined by pairs of stats, as per the below diagram.
The format used in the Chao community to describe evolutions is Alignment / Evolution Type / Secondary Type. For example, “Hero/Run/Power” is a shorthand way of saying that a Chao has evolved into a Hero Run type evolution from its cocoon, and then has been given Power type animals in it’s adult life.
The adult transformation is just like the gradual change that a child Chao goes through before it evolves, with only a few differences: it is a longer, slower process; and it ends with the Chao’s death, not with a metamorphosis (cocoon evolution).