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SONIC CHAO
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To get a Sonic Chao is much more harder to get than a Shadow Chao.

Hatch your chao first. To get your chao into a Sonic Chao it has to evolve into a Neutral chao if it evolves and your like "Its hardly changed", it has don't panic. To keep it Neutral, make a cycle, First care for it with Sonic, then with SHadow, Sonic, Shadow, Sonic, Shadow. That will keep it going Hero or Dark.

You need to give it green chaos drives and green color coded animals, to raise its speed. I recomend going to City escape and Radical Highway, you can get plenty of green type power ups.

Keep doing that and your chao should grow spines which will grow longer eventually.

When your Sonic chao evolves, the orb on his head wont change, but the spines on his head will grow longer, and he will be green, that is a Semi-Sonic chao.

Keep doing that and when he hits age three, by then he should be blue, congrats! You got a Sonic Chao.

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SHADOW CHAO
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A Shadow Chao is a lot easier to grow. You only need to use Shadow for this so its easier.

Give it green chaos drives and green color coded animals, and yes they're will be spines, but the spines will be a tiny messed at the tips. When it evolves, it should be a Dark Chao and his spines should be like Shadow's, but green.

Again. This is a Semi-Shadow Chao.

Keep doing this and when he hits three, his spines will change red. You got a Shadow Chao!