Tails adopts a cute and fuzzy pet named Walter who turns out to be a black hole who sucks up everything in Mobius. Realizing that Walter is from another dimension our heroes have to return him.
Sonic turns detective to solve the mystery of his missing Red Sneakers--and just in time to get them back and stop Dr. Robotnik's latest attack on a peaceful Mobius village.
A group of Freedom Fighters is obliterated by a swarm of metallic fly-bots. When Manic goes looking for the insects, he is stung with serum.
The Hedgehogs steal historical artifacts of Mobuis from Robotnik before he can pawn them off at an auction.
The Hedgehogs find out that Sonia has inherited a castle. She basks in the idea of having a castle for headquarters.
Robotnik organizes a track meet to lure Sonic into a trap.
Sonia is invited to a debutante ball, but before she can be officially announced to society, she and her brothers, Manic and Sonic have an important mission.
Santa Claus has made an announcement - he is retiring and has picked the perfect successor - "Robotnikclaus"! Sonic and his sister resolve to persuade Santa to return and set Christmas straight. When the two track down the Santa who made the announcement, they discover he is just a phony robot and the real Santa Claus is being held prisoner.
Sonic attempts a solo rescue to prevent prisoners from being roboti-sized and is hit by a Memory Scrambler that erases short-term memory.
The Freedom Fighters run into a Swashbuckler, named Ari, battling Swat-Bots. Sonic diverts them, allowing Ari to escape. After hearing that Robotnik is holding his band of Freedom Fighters hostage, Ari decides to help Sonic free them.
The Freedom Fighters, with new addition, Dulcy, develop a De-Roboti-sizer and try it out on Bunnie. It's a success and, against Sally's wishes, Sonic battles Robotnik's newest weapon, a Virtual Reality Shriek-Bot.
Sonic reluctantly takes Tails with him to the Big City to find some cotter pins for the Freedom Fighters catapults. While in the City, Sonic is nearly eaten alive by his old dog Muttski, now a roboti-sized guard dog in the Junk Heaps
Robotnik severely upsets the ecosystem above and below the surface, when he sends explosive, Robotnik snake probes drilling deep under ground in search of oil lakes.
When Sonic and The Freedom Fighters take out Robotnik's main computer, they're trapped by Swat-Bots in an underground tunnel, only to be rescued by a handsome teenager named Griff. Griff takes them deep beneath the Big City.
When Sally uncovers Robotnik's plan to seed the cloud with toxic rain, they attempt a daring mission to sabotage the dirigible-like craft being transported by land vehicles. Mission fails when Sally, Bunnie and Antoine are captured.
Robotnik organizes a track meet to lure Sonic into a trap.
Sleet and Dingo plan to collect the taxes owed to Robotnik from the Duke of Velcronia but keep it for themselves.
On a trip to Port Mobius, Sonic, Manic and Sonia are told that ships are sinking due to the Mobian sea-beast.
Sonic becomes aggravated that maybe their efforts of fighting for freedom seem pointless. Sonia suggests that they go to the Oracle for advice.
A speed enhancing fluid deemed Sonic Tonic is created by Robotnik to make him as fast as Sonic so that he may finally catch him.