Prologue - Mobius
We start with a view of an ancient civilization in a planet called "Mobius", this civilization looks to be made of anthropomorphic hedgehogs who live on island they call "Christmas Island", after that it cuts to a giant ship in outer space where a dark figure with one eye stares at the civilization via a camera in the ship before releasing a nuke, which lands on the civilization, engulfing the island in a massive explosion.
After the explosion, a smaller ship is deployed from the giant ship and lands on the island, where two brain-like aliens with one eye start looking around and find mutated versions of the anthropomorphic hedgehogs, in the midst of it all they spot a baby hedgehog who's been mutated to look blue as well as having othere distinctions from the rest of the hedgehogs, the aliens take the baby hedgehog along with other mutated hedgehogs and go back to their ship.
After that, the game cuts to a laboratory, where the brain-like aliens are mistreating the mutated hedgehogs and experimenting on them, including the 3-year old blue hedgehog, called "Sonic" by the other hedgehogs, who seems to have gained incredible speed due to the mutation. After the experimentation, the hedgehogs are locked into a cell, where a group of mutated hedgehogs who are dubbed by the rest of the mutated hedgehogs as "Freedom Fighters" have started an escape plan, they start putting that plan into action but are caught by the Xorda and only very few manage to get to the escape pods, Sonic being one of them.
The game then cuts to the events of Sonic the Hedgehog 1, in which Sonic races to the evil Dr. Robotnik's base located in "South Island", where he has turned all animals into deadly robots against their will and defeats him in his Egg Piston machine, after which he escapes, but Sonic manages to hit his Egg Mobile one last time, making it leak gas and crash some time later in "S-Cape City", where he's arrested by the authorities. When interrogated he claims that he just wanted "the stone" hidden in South Island so he could save the city from "a bigger threat", but nobody believes him and he's still arrested for animal cruelty and endangering the island's ecosystem.
Meanwhile, Sonic is rewarded by the city mayor and given a medal for his efforts before returning to South Island, his new home, where he decides to rest up for the rest of the day, however, a dark figure similar to the one from his past is secretly watching him, along with many other parts of Mobius, they're planning something massive, something much bigger than what anyone expected...
Chapter 1 - Heads or Tails?
The game plays similarly to the cancelled Sonic-16 for the Megadrive and LittleBigPlanet, players can control Sonic in a 2D environment and move on both the foreground and background, however the actual structure of the game is very different than that of any other Sonic game. Instead of normal Zone-to-Zone gameplay, every Zone is connected into one big world map which you can explore in metroidvania style any time you want, of course some areas are locked off until you get to a certain point in the game but a lot of the Zones are avaivable from the start.
Sonic has a lot of abilities from past games that have been reworked to fit the new formula but he also loses a few, for example in this game he loses the homing attack ability, but he can still Air Dash, Wall Jump, Double Jump and even Spin-Dash, though this time it can be charged up and aimed. However, Sonic also has new abilities such as the "Earth Slam" in which, while mid-air, Sonic slams himself in his ball form down to the ground, destroying enemies below him, and the "Super Spin Attack" which is actually a reworked version of the Instashield ability from Sonic 3 which is triggered by pressing the attack button mid-jump right as one is about to hit an enemy, if done correctly a small shield around him is created for a brief second, which deals more damage to the enemy.
In this game, Rings do not work like they did in past games, where they acted as health for Sonic, in this game Rings work as currency and Sonic instead has his own HP, though Rings can also be used as weapons thanks to Sonic's "Ringthrowing" ability, which allows him to throw a Ring at an enemy to temporarily stun him, and be used to defend himself with his "Ringshield" ability which allows him to spend 20 Rings to make a shield to protect him. When Sonic receives too much damage by one attack he drops a small amount of Rings, as a reference to classic Sonic games.
Power-Ups from past Sonic games return but have several modifications made to them to fit the new structure, while some of them are still found in "Item Monitors", which are scattered throughout the Zones and some of them are randomly generated every so often when you revisit the Zone, however other Power-Ups are obtained as loot dropped by enemies and others are bought on shops, instead of being activated instantly Power-Ups are stored in your Inventory and are activated by touching them in the controller screen, due to the new RPG elements Power-Ups have been reworked, for example Shields, which used to act as an extra hit point, now add a certain amount of HP to your health bar, in other words, your actual health won't be affected until the shield's HP is depleted.
Sonic in this game has a "Chaos Gauge", if he defeats a lot of enemies without being hit, his Chaos Gauge will sart filling up with each enemy he takes down, if the bar is completely filled up Sonic will get to choose one of 3 "Chaos Abilities", the first is "Needle Blast", in which Sonic jumps in the air and shoots his quills out as projectiles throughout the screen, dealing a good chunk of damage to enemies it hits although it requires precision and correct timing, the second is "Health Miracle", in which he regains a big amount of HP, and the third is "Twin Flash" in which for a short amount of time Sonic becomes faster and gets an after image that follows him around and, if he attacks enemies, the after image will do so too, dealing more damage.
Sonic's stats increase throughout the game as he fights enemies and collects "Blue Rings" which are slightly bigger and have small crystals inside of them, these function as XP and can be spent to level up Sonic's individual stats, that way players can customize Sonic in the way they want. However there's another important factor when it comes to Sonic's stats, "Rune Stones", in Chapter 2 Sonic gets a "Runic Reader", a mechanical add-on that is placed on Sonic's arm and can channel the mysthical power of the Rune Stones into his body so he can get its benefits without having to train to be a wizard, you start with 3 slots to place Rune Stones in your Runic Reader (but you can complete sidequests throughtout the game to raise the amount of slots up to 5), each Rune Stone has its own "Mystic Power" level, if the combined total of Mystic Power between all of the Rune Stones equipped exceeds the capacity of the Runic Reader, the amount of magic energy will wear Sonic down and cause a number of negative effects, which is why the player is encouraged to use Blue Rings to upgrade the Mystic Power stat so Sonic can hold more powerful Rune Stones.
Rune Stones themselve provide several different benefits depending on what Rune it is, the effects are varied and range from "Higher attack stat" to "Rings thrown at enemies cause burn effect" to even "Enemies drop more healing items", there are also "Paired Rune Stones", which have better effects but in order to work you must find both of the Rune Stones and slot them into your Runic Reader at the same time. Rune Stones are either found in hidden Item Monitors, dropped by enemies (rarely), bought at the "Mystic Altar", or obtained in sidequests as rewards.
Throughout the game there are also "Warp Booths", which are small rooms containing a small booth which have a stand with a small screen on the end of it, the screen is actually a computer which you can use to save the game, warp you back to the nearest "Safe Zone" (which are cities, towns, havens and other areas in which no enemies can attack), deposit or withdraw rings from the bank as well as Power-Ups and warp to other Zones. These Warp Booths act as checkpoints of sorts, as once you access one you'll get the ability to warp to that Zone from any other Warp Booth or Safe Zone.