You mean Sonic Adventure DX Directors Cut? That one was easy cheesy, sure there were a few hard ones but overall it was easy just as part 2 was. I'd have to say the old sonic series were the hardest especially if Sonic fell underwater and you'd have to either find an air bubble or get out somehow.
As for the Chao's there's many ways to make them, actually theres 4 different types, and 5 if you hack the game...
For a Dark chao, is the same way with an angel chao only instead of a hero character use like Shadow, Rogue, or Eggman and turn the chao dark.
Then theres the Phantom Chao, its sorta like an invisable color however as I found out there's only 1 way to make these and has a 50/50 chance, you'll need a specific chao of any color normal/shiny then another of the opposite you got that was shiny/normal. When these 2 chao's proceed and do there little mating dance thing, there egg when you hatch it (throw it to open I usually do.) The Chao should be Clear as water, almost invisable depending on the color.
Then there's the Chaos Chao, as you had described earlier, yes they require all 21 animals, no chaos drives, they must be at least turned back into a baby chao twice, and Dark/Hero trait fruits depending on how you want your chao. And make sure that they only eat the right fruit, if they ate a normal one or the other type, then it has a chance to prevent them from changing into a chaos form. I know this for a fact because it happened to me, I left my chao garden running when I went afk from the game while caring for them, and when I came back the particular dark chao I had been raising was eating a normal fruit... So I had to wait a whole nother chao reincarnation. And for those that didn't know theres a small cheat to get infinate Chaos Drives after you've obtained them. Say you got 5 green drives and 5 power or whichever, or 2 of each color. If you don't just give it to your chao directly you can manage to keep the drive however this takes patience especially if your chao is eager to move around. First, take the drive you want, then place it infront of the chao without making him have it directly, you'll know when this works because the chao will drink the chaos drive and bounce back and still be there to use it over and over again. I did this many times and have gotten my chaos all to 99 speed,flying,running,power,stamina. Sure it took a very long time especially for a full chao garden. And I had to go redo a few missions to get more drives, if your looking to get drives easily without having to complete a whole mission, use Tails' Prison Break mission or something like that if you choose to use Hero, if you want the dark chao, go to eggmans first mission where he finds Shadow. Hope this was helpful. If you need further advise let me know, I'll help in any way possible.
Now I have a slight question which is related to Sonic Adventure 2 Battle missions, How in the world do you save the chao on Rogue's mission where Eggman Orders Rogue to obtain the Chaos Emeralds. The mission is to find the chao which is on a high platform at the highest point in the map. I've tried everything around it even the mystic song that you play. As well as found her Scope which enables Rogue to see invisable stuff. Anyone know how to get that chao?
Oh yeah, I almost forgot. There's a fun and special few episodes for all you Mario/Sonic fans. It's called Super Mario Bros Z, it has mainly every Mario character in it and Sonic and Shadow as for the rest of there buddies...I can't tell..it'd spoil it. You'll have to watch it. Alvin Earthworm has made these Super Mario Bros Z Shows. I'm still waiting to see what happens next on the last one. But I'd recommend you guys and girls watching it. It's really hilarious on most of the episodes. (Poor Luigi...HAHAHA)