The Wii game NiGHTS Journey of Dreams features a mode called My Dream that functions a lot like the Chao gardens from Sonic Adventure titles. You round up Nightopians and Nightmarens from the levels in paraloops that transports them to the Dream Garden. From there you can feed them blue chips gathered up in the levels and interact with them a bit.
And like the Chao gardens there seems to be a ton of obscure and strange things that can happen such as breeding your Nightopians and Nightmaren together to create "Mepians" that have special animations and activities. These can then also be cross bred and you wind up with Mepians with tons of mixed and matched parts and behaviors. The land itself also seems to terraform depending on... things. Playing levels repeatedly seems to bring in bits of background art like statues from the levels into the Dream Garden. Similarly the grass and plants look more nice and angelic or dark and evil depending on the ratio of Nightopians to Nightmarens and how happy each group is, I think. Hills and streams and the ground level also can change.
However, unlike the Chao garden that is more or less completely understood now, My Dream is still fairly mysterious. For example, there is a so call "King Pian" or "Super Pian" that is bred from Mepians and who constructs a tower of sorts in the level. The exact conditions for obtaining this aren't particularly well known or tested, though anecdotal evidence is found relatively easily. Additionally, there are 4 "stamps" that can appear in your Dream Journal, essentially the statistics page for the game, that seem to be linked with My Dream. Supposedly, 1 of them is earned when you breed the King Pian, and another seems to be linked to the overall happiness of your garden. The conditions for each are still not very well known though. The last 2 seem to be completely unknown with no information available online about how to obtain them. The mechanisms for having level objects appear in the Dream Garden and terraforming in general also don't seem to have any information about them online.
If anyone could hack NiGHTS Journey of Dreams and write some sort of guide on how these things work, especially the stamps, based on the game's actual code, that would be a huge boon to the few people who actually care about this game.