I want to start off by saying I have no experience with modding and all images in this thread are made by me for demonstration purposes. If anyone wants to help me make this a reality, or if you simply have ideas that you think would fit please don't hesitate to contact me.
Despite the controversy over whether the Sonic Adventure games are really that great one thing that most people seem to agree on is that the Chao Garden was awesome. With how much of an open game Minecraft is it's pretty surprising that a good Chao mod hasn't been created already. My idea is that you can raise and breed chao to have different stats, and then equip them to follow you around and give you certain buffs. These buffs can be incredibly powerful but to get anything good you may have to spend many hours getting the perfect Chao.
The first thing you will likely notice when in a new world is that all hostile mobs have a small chance to drop a Chaos Drive. These drives are the key to hatching and raising Chao, so it may be a good idea to make a mob farm!
on very rare occasions you may find dormant Chao eggs that spawn randomly around your world. Depending on where they are found they will look different and require different conditions to hatch. No matter what type of Chao egg you find, they all require large amounts of Chaos energy in order to hatch, that's where the Chao Gardens come in.
Fake Chaos Emeralds / Basic Chao Gardens
In order to create your first Chao Garden you need to flood the area with Chaos Energy. The easiest early game way to do this is by combining an emerald with 8 any colored Chaos Drives to create a fake Chaos Emerald. Placing it into the world will give you a 9 by 9 by 9 cube where you can place eggs and if the conditions are right then they will slowly start to hatch. Different eggs require different blocks in order to hatch, for example an overworld Chao requires large amounts of grass, cave Chao require stone, aquatic Chao require water, etc. Some Chao are even pickier, requiring a certain dimension, altitude or biome in order to hatch. While you can place more then one fake Chaos Emerald to expand the area, some of the higher level Chao require more energy then they can put out, meaning later you will have to use Chaos Emeralds, Super Emeralds, or the Master Emerald to create much larger and more impressive gardens, I will go more into how to get those later.
Even within the same type of Chao there are many different looks that they can be born with. Above are just a few of the possible looks for a neutral overworld Chao. They can have unique mouths, eyes, eye color, head shape, markings, attitudes, etc (look at Sonic Chronicles for some of what I'm thinking). My hope is to have presets that can be randomly mixed and matched to create thousands of possible combinations. No two Chao look identical, so if you hatch a cute one you should make sure to take good care of it!
Miles Electric / Baby Chao
In order to properly interact with your Chao (as well as many other things in the mod) you should first craft a Miles Electric using a fake Chaos Emerald. While you can still feed and play with your Chao without one, it is very important if you want to view their stats or get them to do what you want. Right click with the Miles Electric and it will show you everything that can be interacted with within a 20 block radius, including Chao, Chaos Emeralds, and more. It will show a preview of each object followed by their nickname and then their mob name. Click on your Chao and it will bring up their GUI, which allows you change their name and view all of their stats including happiness, attachment (meaning how close they are to you), alignment, the level of each skill, and any abilitys your Chao may have. Each Chao is born with natural skills that can't be changed and learned skills that you can increase in many different ways similar to IVs and EVs in Pokemon. Chao stay in their baby form for about 30 in game days or about 10 hours without skipping the nights and evolve into different forms depending on how they are treated. This may seem long but it gives you time to teach them abilities, change their alignment, and max out their skills. You can either give your Chao Chaos Drives, feed it different types of food, or let it snuggle up to different animals in order to boost it's stats and adjust it's appearance. Stats and training aren't everything though, if you want your Chao to be the best it can be you need to keep it happy and make it love you! The more time you spend with your Chao the more it will become attached, and if you are close enough it may even follow behind you on your adventures or sit on your shoulder! While far to weak to do much to help you, this does keep up it's happiness and depending on what it watches you do it may even pick up some skills along the way, boosting it's stats. There are even some special events that grant Chao unique skills if witnessed, such playing instruments by watching you mess with note blocks, dancing from watching parrots dance, play fighting by watching you kill mobs, etc. If you plan to keep it away from the garden long stock up on Chaos Drives as Chao feed off the Chaos Energy and can grow week or even die if they don't get enough. While mobs won't directly attack your Chao they can also die from drowning, suffocating, or many other dangers that exist in the world. Just like a child it is up to you to take care of them and keep them healthy. Alignment is based off of your own alignment which is a hidden meter that changes depending on what actions you take. Farming, planting trees, breeding animals, etc. bring it towards hero, while killing animals, setting fires, etc. will bring it towards dark. (this point needs a bit of work, if you have suggestions let me know)
What do you get from all the effort? After a long enough wait your Chao will evolve into one of many different adult forms, and lock in the skills you taught them. Depending on what they know they can grant the player wielding them a permanent buff to one of their stats such as mining speed, strength, jump height, etc. They can also grant unique abilities such as elemental shields, have a small chance for attacks thrown at you to miss, make mobs drop more loot, etc. While their abilities may be somewhat minor at first, adult Chao can breed with each other and pass down their genes such as appearance and abilities to make even more powerful Chao with better natural skills.
After enough time (around another 30 days) your Chao will enter it's 3rd stage. Depending on how well you treated your Chao it will either die off or become reincarnated, reverting it to a child and bringing it's stats down to 10% what they were before. This may sound bad but they keep their abilities and the stat cap is raised by 25%, allowing the Chao to become much stronger next go around. This boost caps out at 200% after 4 reincarnations.
In order to upgrade your Chao Garden you first need to acquire a more powerful source of Chaos Energy. Fake Chaos Emeralds are Tier 1, followed by Chaos Emeralds for Tier 2, and Super Emeralds or the Master Emerald are Tier 3. Unlike in the Sonic games there are more then just 7 emeralds, and they are instead only incredibly rare, being just as rare as strongholds. They can spawn anywhere from laying on the surface to burred on the first layer of Bedrock. In order to properly locate these you need to craft an Emerald Radar, which acts similar to a compass and points you in the direction of the nearest source of Chaos Energy. It can pick up multiple signals at once, but luckily things like the fake Chaos Emeralds and Chaos Drives have very small ranges and the signal drops off only a few blocks away. Real Chaos Emeralds have a range of a few chunks, so you will still have to explore around quite a bit before your able to detect one. Once you find one you can place it down just like a fake Chaos Emerald and it will give you a much larger 18 by 18 by 18 Tier 2 garden, where Chao grow faster (25 days instead of 30), mobs are more likely to drop Chaos Drives, and you even get Regeneration 1 while within the area.
Angel Island / Super Emeralds
You want a Tier 3 garden do you? Spawning no closer then 10,000+ blocks away from spawn and being much rarer then any other structure in the game exists 1 Angel Island per world. On it you will find many naturally spawning Chao as the whole island is already classified as a Tier 3 Garden and in the center of the island you will find a large shrine with the Master Emerald in the center and 7 pillars around it. You can feel free to grow your Chao here and they will grow much faster then even with the Chaos Emerald, only taking about 20 days to grow to adulthood. While on the island you will get Regeneration 2 and all effects that the Chaos Emerald give are doubled, however the Master Emerald cannot be moved and the chunks the island inhabits cannot be edited whatsoever outside of placing eggs (this stops people on servers from ruining it since there is only one per world). If you want your own Tier 3 garden start by placing 1 Chaos Emerald on each of the pillars around the Master Emerald and stand on top of the Master Emerald. Lightning will strike each of the 7 Emeralds turning them into Super Emeralds which can then be placed into the world to create huge custom Tier 3 gardens with all the effects found on Angel Island. Super Emeralds have a range of 30 by 30 by 30 and you get 7 so it is very unlikely you will run out of room, and you can also place these around your world simply for the beacon like effects they give. Super Emeralds can be used in any recipe that requires a Chaos Emerald.
Miles Electric 2.0
You can try to find Angel Island with the standard Emerald Radar but if you want a more reliable way then your best bet is upgrading your Miles Electric by combining it with a Chaos Emerald. This acts as a mix of the two previous devices however unlike the standard Emerald Radar, the Miles Electric 2.0 has no maximum range, detecting the closest object even if it's hundreds of thousands of blocks away. You can also switch it's mode, telling it to look for a specific type of object such as the Master Emerald and ignore all others. This makes finding what you want to much much easier than before, which is great both for getting the 7 emeralds you need and for finding the island itself. You can also right click an emerald directly to exclude it from the search.
Under very special circumstances a Chao may reincarnate into a Chaos Chao, boosting all of it's stats and making it completely immortal. Chaos Chao are achieved in very similar ways to how they were in SA2: At least 2 reincarnations, high happiness, ate at least one of every food, snuggled at least one of every animal, and absorbed at least one of every Chaos Drive. The only difference being that the stats don't have to be equal, as it will grant buffs depending on it's stats just like any adult Chao. An added requirement is that you must have a level 3 Chao Garden in order for this to take place.
Machine Core / Advanced Machine Core
Basic cores are crafted with a Fake Chaos Emerald surrounded by redstone and the Advanced is the same but with a real Chaos Emerald. On their own they are useless, but machine cores are used to craft various other electronics.
Surround an advanced machine core with cobblestone and you get yourself a Chaotic Furnace, which is double the speed of a regular furnace and uses Chaos based items to run. Chaos Drives can cook 4 items, Fake Chaos Emeralds can cook 100 items, Chaos Emeralds can cook 1000 items, and a Super Emerald will make the furnace run forever.
Buzz Bomber / Moto Bug
Both are crafted with basic Machine Cores and a various assortment of gold, iron, and redstone. Buzz Bombers are flying Badniks with a gun and Moto Bugs are ground based melee attackers, both act as a sort of "pet" that will do their best to protect you. You can right click them to change them from stationary to follow mode and back again. In stationary mode Moto Bugs will attack any mob in a 10 block radius before returning to their "home", and Buzz Bombers will do the same but will fire on enemies 20 blocks out. In follow mode they will basically do the same thing but follow shortly behind the player like a dog and teleport if they get too far behind. By default they will attack everything except their owner (including other Badniks), but can be edited with the Miles Electric to customize who they do and don't attack (this can include other players). They have relatively low health and you can feed them Chaos Drives to heal them, but if they do end up defeated they have a 100% chance to drop a random Chaos Drive. Other Badniks like the Egg Pawn, Swat Bot, Crabmeat, etc may be added if there is enough demand.
Crafted with a basic machine core, some lapis, some iron, and some redstone, Omochao is an annoying creature that will follow you around and tell you useless facts you already knew. While pretty much useless it can be a fun way to mess with people. When defeated it has a 100% chance to drop a random Chaos Drive.
Crafted with a Omochao, some gunpowder, some redstone, and some iron, the Omochao gun is a ranged weapon that can be charged by right clicking and fires by letting go similar to a bow. It takes 1 Chaos Drive per shot and has slightly worse range then a bow, but it more then makes up with it with a large amount of damage (about the same as power 2) and being able to bounce off walls up to 2 times until disappearing. It can't be enchanted so in reality it isn't all that useful but hey, It's bullets resemble it's head, what's not to love?
Chao Races / Chao Karate
I would love to add these along with their prizes and medals to the game but i can't think of a way to do it properly. Best i can come up with is crafting markers to create your own arenas but i'm not entirely sure.
The Dark, Hero, and Neutral Chao Garden themes from SA2 are added as music discs, alongside the Lobby music, Chao kindergarten, Live and Learn, and various other Sonic songs. They can be found in the same way as vanilla music discs, dungeon chests or a skeleton killing a creeper.
Combining an advanced machine core with some gunpowder, 2 diamonds, and some iron will allow you to sail through the air majestically, like an eagle. pioliting a blimp. It may not be fast but you have way more control then with an elytra and you don't have to worry about loosing speed. If you need to go faster you can right click to use up one Chaos Drive and boost relatively quickly for a short distance.
Chaos Emerald Minibar
While you aren't an embodiment of Chaos like Sonic or Tails, that doesn't mean you can't take advantage of the power of Chaos! Crafted with a Chaos Emerald, two Brewing Stands, and a few pieces of wood, the Minibar allows you to mix together different ingredients alongside Chaos Drives to create different foods and drinks such as the Chaos Emerald Mocktails (collect them all!), Chaos Cola (both "Here We Go" and "Primal Venom" flavors), POW Candy, POW Drink, POW Gum, Speed Bar, Rock Candy, etc. Each item gives a different usually short lived buff similar to vanilla potions.
Chao can be equipped with different articles of clothing that can boost defense, apply buffs to it, or simply look nice. there's a large variety of different hats, vests, shoes, pants, etc, including every type of player armor. There are also unique pieces that can be found in dungeon chests or won from events such as the Eternal Bowtie which looks like the one wore by Cheese and stops your Chao from evolving or growing it's stats.
And that's about it! I want to add other things to do with the Chaos and Super emeralds but can't really think of anything. The only things that they're used for are transformations, power boosts, powering machines, and occasionally weaponry, all of which except transformations i pretty much have covered. Let me know what you think, and if you have any suggestions or even want to hop on and help me make this real then please please please let me know, I'll make an effort to read any comments posted here. Thanks for reading!