Thought I'd give nearly the whole Sonic cast a redesign, altering their backstories and appearances by attempting to combine elements from every form of media in the franchise (video games, comics, and movies), giving them my own spin.
Sonic the Hedgehog
Born with a mysterious power that gives him super speed, Sonic was raised in the resistance by his uncle Chuck and his mentor Longclaw after his parents (the previous leaders of the resistance) were murdered in an Eggman Empire raid on Green Hill Village. Taught on how to control his gift, Sonic uses his abilities to wonder the world in his youth, saving anyone he finds from the Empire's robots despite his guardians telling him to hide his power. After meeting a certain young fox and accidentally leading an Eggman Empire platoon to the Resistance base, Sonic tapped into the true potential of his power to wipe out the robots and soldiers and escape with his new friend, leaving him as the only free Resistance member left in the world. Now he and his new friend, now brother, must search the world for the legendary Chaos Emeralds to fight back against the Eggman Empire and free the world.
I know he doesn't look that different from the original design, but other than giving him a scarf (which looks good on him), I could not think of anything else.
Miles "Tails" Prower
Miles Prower is one of the twin sons of Sylas Prower, one of the Eggman Empire's Chaos Council. Born with a mutation that gave him an extra tail, he was mocked by his twin brother and abused by his father for it, forcing him to try and hide his secondary tail by tying his tails together. Despite being raised in the Eggman Empire and buying into the propoganda, young Miles had a kind heart and a love of nature, which did not sit well with Sylas, who tried his best to mold him into a perfect loyal member of the Eggman Empire just like himself and his brother. After Sylas utterly wrecked Miles' magnum opus (a biplane, as he was interested in flying) because he saw it as a distraction, Miles secretly ran far away, hoping to escape the abuse. Alone and hungry, Miles got lost in a forest, where he met a blue hedgehog named Sonic, who comforted him and brought him to what Miles realised was a Resistance base, where he realised that he was on the wrong side. When an Eggman Empire platoon led by Sylas attacked the base tracing the tracker on the fox's uniform, Miles proved his allegiance by rescuing Sonic from his father, using his twin tails to propel him into the air and crashing onto the robots. After escaping with Sonic, Miles began to see him as an older brother, who reciprocate by unofficially adopting and giving him a nickname to break away from his past, Tails.
I really like Tails' design in Sonic Boom, as it matches his background as an engineer and an aviator, so I gave him goggles. I also gave him a cape that matches the one wore by Classic Eggman, boots to match Modern Eggman, but blue, and a button on his belt, as a reference to his past as a former junior member of the Eggman Empire (in this universe, anyway).
Knuckles the Echidna
No one knows where Knuckles came from, not even Knuckles himself. He woke up one day with no memories, save for a green gem shard he carries around on his hat. Knuckles travels the world trying to piece together his past and find out if there are other Echidna like him, but came across an unusual pair consisting of a blue hedgehog and a two-tailed fox, the former of which feels familiar to him for some reason. After a misunderstanding that led to him and the Hedgehog coming to blows, they were attacked by the Eggman Empire, who were looking to steal the shard Knuckles was carrying. The trio fought the army off, resulting in Knuckles gaining a small respect to the Hedgehog, who was called Sonic, leading him to join up with him and his partner on their quest, which might lead him to some answers to his past.
I wanted to give Knuckles a more tribal vibe, so I gave him some white face paint (not cover his face with it, just small markings that are noticeable). I also gave him some bandages for his arms and legs, as a reference to his Boom design as well as his status as a fist-fighter. The hat is a reference to the Sonic OVA, but I envisioned it making him look like a wanderer.
Amy Rose
The latest in a long line a magical sorcerers from Little Planet, Amy Rose is kind and gentle to anyone she meets, but has a massive temper that can lead her to swing her hammer at whoever ticked her off like a maniac. After meeting Sonic during his trip on Little Planet, Amy developed a crush on him, wanting to join him on his adventures, but is too shy to confess. She joined Sonic and his team (with her family's blessing) after the Eggman Empire attacked Little Planet, trying to harness its mystical energies for themselves, but they failed thanks to her. Now she her hammer and magic (mainly her hammer) helps Sonic and his friends in finding the Chaos Emeralds and dismantling the Eggman Empire (while also trying to win Sonic's affections).
Amy was actually difficult to redesign, but I think I managed to do well, combining her modern design with her boom design in the dress. The green jacket is a reference to her classic look)

Made in Kisekae, feel free to ask for codes if you want to use the models (But NO NSFW PLEASE!)
Sonic is property of SEGA