This is a summary and overview of the differences between the various Chao systems.
Sonic Adventure (Dreamcast)
This was the first game to ever feature Chao, and thus had the most basic system compared to later games. The Chao Garden had only a few- now standard, features: giving Chao fruits and animals, showing affection with each character, branching evolution based on skills, and racing. There were very few breeds of Chao, and the garden contained many inhospitable landscaping features.
There was also an exclusive mini-game called Chao Adventure that was played with the Visual Memory Unit (VMU). The game was accessed by placing the Chao in the VMU transfer machine found in each garden, and you would be able to play the game on the portable VMU away from the Dreamcast. Many prizes could be obtained on Chao Adventure that could be transferred back to the Chao Garden, as well as raising the Chao's stats within the mini game itself. This was also the only way to name the Chao and also the only way to look at the Chao's attributes.
Sonic Adventure 2 (Dreamcast)
The sequel introduced the player to new gardens as well as an improved system for raising the Chao, cleaning up some glitches. The Chao Kindergarten was introduced, giving the player the Classroom to teach Chao special skills, the Principal to give advice about raising Chao, and a Doctor to check up on sick Chao. The player interactions were also changed, as playable characters were divided into two groups, Hero and Dark, which directly influence the Chao's own alignment when shown affection. This resulted in an even wider branching evolution system with over triple the amount of obtainable Chao evolutions. Chao Racing returned bigger and better than ever.
Chaos Drives to raise stats without changing your Chao's appearance, and different animals were also added to the game. This, the Kindergarten and the different Chao Gardens are all game-specific. These additions were gone in Sonic Adventure DX, but back in Sonic Adventure 2 Battle (see the sections below).
Using the Dreamcast's connection to the web, players could also obtain special breeds of Chao from an online Black Market. The player could also leave Chao in an online Chao Daycare, where they could exchange Chao with friends. This service has since been disabled following the end of life for the Dreamcast.
The VMU mini game also had a sequel, Chao Adventure 2, updating the visuals of the Chao Adventure, but essentially remained the same experience as its predecessor. While Chao Adventure can be used to take Chao to Sonic Adventure 2 (with glitches), Chao Adventure 2 is only compatible with Sonic Adventure 2.
Other differences from the Sonic Adventure Chao system were the addition of two special stats only raised via playing Chao Adventure 2 on the VMU: Intelligence and Luck. These stats affected your Chao's ability to solve puzzles and avoid traps in the races.
Sonic Adventure 2 Battle (GameCube)
Sonic Adventure 2 Battle was the port of Sonic Adventure 2 from the Dreamcast to the GameCube in 2002, and it included an overhaul of the Chao system. The game uses the same engine, with slight modifications to clean up any glitches, including entirely modifying the landscapes of the Chao Gardens (albeit making them smaller than the Dreamcast versions).
Major changes were due to the lack of the web access and VMU found in the Dreamcast version. The Chao Kindergarten was changed significantly to cater for this.
- A Chao skill/status table appears when you pick the Chao up or feed it. (stats could only be seen inside the VMU mini game Chao Adventure 2 on the Dreamcast).
- The Kindergarten now included the Black Market, which would sell fruit and seeds, previously obtained from Chao Adventure 2 only.
- A Fortune Teller was introduced to allow the player to easily name their Chao, or have it assigned a randomly chosen name (again only able to be done before via Chao Adventure 2).
- The Chao VMU Transporter was replaced with a Game Boy Advance trasporter. Instead of Chao Adventure, you could transfer a single Chao to a Tiny Chao Garden mini game on specific Sonic Advance Gameboy Advance games. The new Chao Transporter also came with a function to move Chao between memory cards, as well as an option to delete Chao, in order to make room for more Chao in the garden.
The new Black Market also sold new special Chao eggs, as well as headgear for Chao to wear. The Chao Doctor would also now give a more detailed skill status chart, including the Chao's personal interests and achievements in competitions.
Chao Racing was also supplemented with brand new Chao Karate, a game-type in tribute to the fighting from the original VMU mini games.
Sonic Adventure DX: Director's Cut (GameCube)
The orginal Sonic Adventure was ported to the GameCube in 2003, and titled Sonic Adventure DX: Director's Cut. Although the port kept the game-specific features from the first Sonic Adventure (original animals, no Chaos Drives), it kept the updated Chao system from Sonic Adventure 2 Battle and left it intact for the most part. There were a few essential modifications.
- The VMU Chao Transporters were changed to be like the ones in Sonic Adventure 2 Battle. The feature that moved Chao between memory cards was replaced with a feature to name your Chao.
- The Black Market was introduced to the Station Square Garden, behaving just like the one in Sonic Adventure 2 Battle, except not selling seeds as they could not be planted in the garden.
- The Black Market also continued selling Hero Fruit and Dark Fruit, becoming the only way on Sonic Adventure DX to adjust a Chao's alignment since there were no separate Hero/Dark characters in the game unlike Sonic Adventure 2.
Sonic Adventure DX: Director's Cut (PC)
Sonic Adventure DX was ported to Windows in 2004. The Game Boy Advance connectivity was lost, and thus the Chao Transporter was replaced with a Chao Name Machine. Overall the game was identical to it's Gamecube counterpart, with one unexpected graphical change involving Shiny Jewel Chao appearing to look different.
Sonic Adventure DX: Director's Cut (PS3, Xbox 360)
Sonic Adventure DX was ported to the PS3 and Xbox 360 in 2010. Originally believed to be actual restorations of the Dreamcast version of Sonic Adventure, the games are simply ports of the PC version cleaned up a little bit. The only noteworthy change is that in breeding mechanics, leaving some players disinterested.
Generation 2 Remakes
Sonic Adventure DX (PC - Steam)
Sonic Adventure DX was released on Steam for PC, there were a few differences to the non-Steam SADX released from PC, such as two-tone Chao being unobtainable.
Sonic Adventure 2 (PC - Steam)
Sonic Adventure 2 was released on steam with the "Battle" content avaliable for purchase separate. The DLC does not change the Chao system for this game, which remains as the Gamecube Generation 2 Chao system. Shiny two-tone Chao look different and are refered to as "Bright Chao" by the community. Several other bug-fixes were added.