Following the discovery of the city of Ursalia in Season 4, Season 5 focuses on the uneasy alliance between the peaceful Gummis of Gummi Glen and the warrior-like Barbic Gummis.
Tummi takes pity on Doctor Dexter, an unsuccessfull pharmacist, and decides to improve his concocctions with a shot of Gummiberry juice. Unfortunately, this new wonder medicine also attracts the attention of Igthorn, and without the knowledge of how to exactly replicate the formula, the Doctor is caught between a rock and a hard place.
Sunni learns the importance of keeping Gummi traditions when a giant reawakens thanks to her carelessness.
Gruffi burns the Great Book of Gummis and goes to Ursalia to find another to replace it. Their he meets Thornberry, a gummi who tries to save Ursalia from an evil witch, Lady Bane!!
Gusto inspires delusions of grandeur into Gruffi's bridge project.
Duke Igthorn meets Lady Bane for the first time and falls in love.
Tummi fights a battle with his own self control when Duke Igthorn temps him with food.
When rules don't seem to have any effect, Cubbi learns an important lesson of life from Gusto by living with him for one day.
Gusto inspires delusions of grandeur into Gruffi's bridge project.
King Gregor hosts King Jean-Claude, a ruler of a nearby Frankish kingdom, and his daughter Marie in order to improve diplomatic relations; but both Sunni and Calla learn that being a princess does not make one an instant sweet little girl. Even worse, Marie's haughty attitude eventually causes King Jean-Claude to stage a military siege on Dunwyn.
Gusto creates a lifelike stone statue of Zummi, then persuades Zummi to come to his workshop so he can create a better one. Meanwhile, Gruffi mistakes the statue for his friend, believing that Zummi has turned himself into stone - and so does Lady Bane.
The Trolls are on the loose again, and this time they've hijacked an ancient Gummi digging machine.
A message by Sir Thornberry lures both the Gummis and Igthorn back to Ursalia, where a new band of Gummis, the Barbics, have taken refuge. The new tenants, however, are mostly a rather unsociable bunch with a deep hatred for all humans. They seek the ultimate weapon in Ursalia to get revenge against the humans, and as it so happens, this weapon is close to falling into Igthorn's hands.
Grammi finds what seems to be a Gummi forced to work as a side show and takes him home to Gummi Glen, but Gruffi thinks there is something wrong with him. Are Gruffi's suspicions correct, or have they found another Gummi Bear?