Professor Von Schlemmer (from Too Tall Tails) has created a machine which brings dreams to life. When Robotnik hears about it, he forces the Professor to alter the machine so that nightmares come to life.
When Robotnik invades Labyrinth, an underwater city, and kidnaps Princess Bubbles, a seahorse-dude named Surff seeks Sonic's help. It seems Surff and the Princess are in love, but the royal family deems Surff "unworthy".
Robotnik installs a new "obedience microchip" in Scratch and Grounder and orders them to drill for a rare mineral in a tropical mountain. With his Freezomatic machine, Robotnik covers the mountain in ice and runs a Hermit out of his home.
When Hacker, an adolescent mole computer whiz steals a super-intelligence program from Robotnik's computer, Sonic has to protect him, smashing Grounder to pieces.
Mobius is suffering a crime spree and all the evidence points to Sonic as the culprit. But the real thief is a lab rat wearing a high-tech vehicle suit who was sent by Robotnik to discredit our hero.
Sonic joins up with a group of Dr. Robotnik's rejects who have been banished to the dump and helps them understand that their shortcomings were really their strenghs.
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.