When your baby Chao cocoons and comes out as an adult, that's first evolution. However, your Chao will continue to change visually as he ages, and as you give him more animals and Chaos drives.
If you keep to one colour of animal or Chaos Drive, your Chao will attain second evolution at about age two. Feed your Chao often and he will change faster. This page contains a descriptive list of all second evolution combinations. I may add pictures at a later date - I know these descriptions ain't the best.
NB: To get the stamina evolutions, feed the Chao but do not give him any animals or Chaos Drives.
Pick your Chao type
Hero|Neutral|Dark
The Hero Chao all have a pure white body colour with pastel highlights. The distinguishing feature is a halo instead of a round ball, and inverted eyes (black iris, white pupil). Hero Chao wings curve down like angel wings.
Hero Swim: a white Chao with a rounded head shape and two little leaf-shapes sprouting from the top of the head. The highlights are pale blue-green and yellow.
Second evolutions:
Hero Swim/Swim: The leaves become much larger and curl down beside the Chao's face as if it has bangs. Highlights are aqua blue and mauve.
Hero Swim/Fly: Similar to Swim/Power in shape, although not so fat. The leaf-shapes become larger and flick up and back; the colour is more yellow-green.
Hero Swim/Run: Similar to the Swim/Swim in shape but with bright blue highlights and a streamlined form. The leaf-shapes become rounded and flop down around the Chao's face.
Hero Swim/Power: Another very fat Chao, with green and yellow highlights, and large sticking-up leaf shapes with a backward turn.
Hero Swim/Normal: Not much change to be seen. Highlights are slightly deeper; leaf-shapes are larger and lift up a little.
Hero Fly: a white Chao with attractive purple highlights and two little feathers sprouting from the top of the head. The wings are large and blue-white.
Second evolutions:
Hero Fly/Swim: Chao sprouts two more feathers. The feathers get a wiggle in them, and the tail becomes large like a beaver's. Highlights are purple, blue and green. Wings gain an aqua tint.
Hero Fly/Fly: The feathers become extremely long, swept-back, and the Chao gains two more of them. The wings become very large. Highlights are the same as the basic evolution.
Hero Fly/Run: The feathers curve upwards and become streamlined; the highlights are the same as the basic evolution.
Hero Fly/Power: The feathers split apart halfway up, and the highlights become a bit more reddish.
Hero Fly/Normal: The Chao gains two more small feathers and gets a bit plumper. The original feathers curl downwards. Color of the highlights deepens.
Hero Run: a white Chao with a long stalk coming out of the top of the head. Highlights are purple and blue stripes with a yellow belly. Quite a striking Chao.
Second evolutions:
Hero Run/Swim: The stalk splits into three large flaps, the body has a flatter shape with green and indigo highlights and a bright green belly.
Hero Run/Fly: The stalk becomes heart shaped :) Highlights are pink and purple; Chao has a slimmer body shape.
Hero Run/Run: The stalk splits into three; highlights are deep blue and aqua, and stomach is yellow.
Hero Run/Power: The Chao gets a kind of bobble at the end of its stalk, and becomes chunky and powerful. Highlights are pink and gold.
Hero Run/Normal: The stalk grows long and splits into three. No change to the highlights.
Hero Power: a white Chao with three spotty red knobs on its head. Highlights are mottled red, and the body shape is rounded and chunky. Wings are very small.
Second evolutions:
Hero Power/Swim: A fat white Chao with deep magenta highlights; two of the knobs are flattened and elongated into flaps, and the third is thin.
Hero Power/Fly: The lumps on the head are very large and pointed, the highlights are purple, as is the chest. Wings are large and blue.
Hero Power/Run: The lumps are tall like columns, spotted peach and yellow, and the chest is pinkish red; the Chao is a bit more streamlined.
Hero Power/Power: Not very different from the basic Hero Power, except for much larger lumps on the head and a deeper red for highlights.
Hero Power/Normal: Almost no difference.
Hero Normal: a white Chao with a round head (no points) and two small rounded bobbles. Highlights are blue stripes and the wings are yellow. The default Hero Chao.
Second evolutions:
Hero Normal/Swim - The round bobbles get larger and sharply pointed, and the highlights become a bright aqua blue.
Hero Normal/Fly - Highlights are purple; the bobbles on the head become extended.
Hero Normal/Run - Highlights are deep blue and aqua rings; the bobbles become squarish, with long pointed extensions.
Hero Normal/Power - Highlights are darker blue and purple; the bobbles on the head are extended and rounded with a narrow waist.
Hero Normal/Normal - Similar to the default Hero but with features slightly exaggerated: the bobbles are larger and the colour somewhat deeper.
The Neutral Chao are the most visually interesting, displaying far more colour variation and a weird range of different shapes.
Neutral Swim: a striking streamlined green and yellow Chao with a long fish-like head. The ears look almost like fins. Shorter than other Chao on account of the flattened head.
Second evolutions:
Neutral Swim/Swim: HUGE ears, right down to the ground! An endearing Chao. Head is very long; colour is deeper blue and green.
Neutral Swim/Fly: The point curls upward and becomes very tall; the body becomes pinkish and pale yellow-green.
Neutral Swim/Run: A bright green/aqua Chao, rather thin, with a flattened aerodynamic shape. The ears are small but elongated and point straight back along the head.
Neutral Swim/Power: Fat!
Neutral Swim/Normal: Chao's appearance just becomes a bit taller/more streamlined.
Neutral Fly: the basic NiGHTS Chao, a pinkish Chao with two long purple-striped points. The wings are large and green.
Second evolutions:
Neutral Fly/Swim: The points turn into thick flat lumpish things and the Chao develops flap-like ears; a very odd-looking, streamlined Chao. Colour is apricot with reddish stripes.
Neutral Fly/Fly: The famous True NiGHTS, purple-striped with large curling points and gigantic golden wings.
Neutral Fly/Run: Points curl round like ram's horns; the Chao is peach in colour with a golden belly and feet. Wings are bright green.
Neutral Fly/Power: A Reddish pink Chao with small wings and a stocky build. The points curl up and over like devil's horns; sometimes called the Jackle Chao.
Neutral Fly/Normal: The points stick out straight from the back of the Chao's head. Colour is mostly the same, but wings are orange.
Neutral Run: a plump lime green Chao with darker green stripes on his three points, and dark green highlights.
Second evolutions:
Neutral Run/Swim: A bright aqua blue Chao with an elongated, streamlined head. Build is very chunky.
Neutral Run/Fly: The points on the Chao's head curl upwards, as do the toes. Sometimes called the Elf Chao. Colour is a soft lavender with paler blue stripes.
Neutral Run/Run: Sonic Chao - a deep blue Chao with black highlights. It gains a fourth point, and the points sweep down like Sonic's spines.
Neutral Run/Power: A fat purply-blue Chao with a chunky shortened head shape and heavy arms. Colour is bright magenta with a red belly.
Neutral Run/Normal: The Chao's body thickens and the color becomes a muted blue with green belly. Points are longer and straighter.
Neutral Power: a bright red chunky Chao with two vertical points, a large and small.
Second evolutions:
Neutral Power/Swim: Chao is bright almost pure red with a very long head shape. Highlights are hot pink.
Neutral Power/Fly: Ears curl upwards as if Chao has devil's horns; the first point stretches straight up. Colour is bright red with deep pink highlights.
Neutral Power/Run: The two points are small and curl backwards; the body colour isn't quite as bright and the Chao appears more streamlined. Highlights are yellow.
Neutral Power/Power: Another heavy, chunky Chao, features just slightly exaggerated from the basic power evolution. Colour is deep red all over.
Neutral Power/Normal: Ears are much smaller; color is deeper and darker. Chao's build becomes a little more streamlined.
Neutral Normal (stamina evolution): a plain blue Chao with one vertical point, similar to a baby but larger with green highlights instead of yellow. The Neutral Normal evolutions are very subtle changes and, in my opinion, not very interesting.
Second evolutions:
Neutral Normal/Swim: The point on the head is larger, and curls up and backward slightly. Color is a stronger hue.
Neutral Normal/Fly: The point on the head curls up and over. Color is a stronger hue.
Neutral Normal/Run: The point on the head is swept back slightly. Color is a stronger hue.
Neutral Normal/Power: The point on the head pushes forward slightly. Color is a stronger hue.
Neutral Normal/Normal: Chao's appearance looks generally a bit thicker and coarser. Color is a stronger hue.
The Dark Chao feature very dark, muted colours with striking highlights, and their shapes are spikier than other Chao. The distinguishing features are a spiked floating ball instead of a round ball, batlike wings, pale eyes with a light blue iris and white pupil, and a pointed devilish tail.
Dark Swim: a dark green Chao with pale green streaks running along the length of the head. The head shape is similar to the Neutral Swim, but the Dark Swim has two points at the back of the head rather than one.
Second evolutions:
Dark Swim/Swim: The Chao's head becomes more elongated and it gains another spike at the back. Colour deepens. The feet look webbed.
Dark Swim/Fly: Not much different in shape, but the colour changes to dark blue, with pale blue highlights.
Dark Swim/Run: An impressive black Chao with ice blue highlights; the spikes curve upwards.
Dark Swim/Power: A plump green and black Chao with three spikes; the head shape is shortened compared to other Dark Swim Chao.
Dark Swim/Normal: Little difference aside from a dulling of the green colour.
Dark Fly: A very dark purple with purple stripes and large batlike wings; looks like an evil version of the NiGHTS Chao. The face is black.
Second evolutions:
Dark Fly/Swim: A very dark blue Chao with straight electric blue tipped points. Highlights are pale blue.
Dark Fly/Fly: Dark NiGHTS Chao: the points become longer and get a wave in them, and the purple colour becomes richer. The highlights are paler purple.
Dark Fly/Run: Mickey Mouse Chao o_O
Dark Fly/Power: The two points flare straight out from the back of the head and then curve in towards each other like mandibles; the Chao is dark reddish purple with pinkish higlights.
Dark Fly/Normal: The points become longer and straighter; the colour dims.
Dark Run: a dark green three-pointed Chao with pale green streaks running back from its face along each point. The points become sharply kinked towards their ends.
Second evolutions:
Dark Run/Swim: Metal Sonic Chao, in shape if not in colour. The points become smooth and swept back; the colour is blackish blue with peach-coloured highlights.
Dark Run/Fly: Similar to the first evolution but the streaks become yellow and the colour is a stronger blue.
Dark Run/Run: The famous Shadow Chao, a pure black Chao with brilliant red streaks. It gains a fourth point; the points flare out to the sides like Shadow's spines.
Dark Run/Power: The Chao is dark blue with electric blue highlights; the top point sticks straight up and the other two curve down over its shoulders, similar to Chaos. The head shape is shortened and looks squashed from the side.
Dark Run/Normal: Similar to the first evolution, but features are more exaggerated and the colour changes with blue tips appearing on the points and the green darkening to black.
Dark Power: a chunky brown Chao with one point sticking upwards, ringed by jagged orange stripes. The highlights are jagged stripes on the arms and a coloured belly. The head shape is actually similar to a Neutral Normal Chao, although more angular.
Second evolutions:
Dark Power/Swim: The Chao is a very dark green, almost black, with paler green highlights; the head shape becomes more streamlined.
Dark Power/Fly: The Chao is very dark purple; highlights are dull red, and another smaller point appears on the head.
Dark Power/Run: A black Chao with dull yellow highlights and a second small point on the head. Slightly less chunky than the other Dark Power evolutions.
Dark Power/Power: Heavier than the basic evolution, with a larger point on the head. The point is kinked, and the Chao's arms gain little spikes.
Dark Power/Normal: Very similar to the basic, but the highlights are purplish.
Dark Normal (stamina evolution): a brownish black Chao with a single jagged point and small batlike wings. The highlights are red. With the second evolutions it's difficult to discern any real difference, but I'll include them anyway for completeness' sake.
Second evolutions:
Dark Normal/Swim: Highlights are orangish instead of red and the point straightens out a bit.
Dark Normal/Fly: Identical to basic evolution, but with a purple tint rather than brown.
Dark Normal/Run: Similar colour to the Dark Normal/Fly, but the point is slightly larger and swept back.
Dark Normal/Power: Almost no difference, aside from a longer point.
Dark Normal/Normal: Slight exaggeration of the basic evolution's features.