Bubda was a hermit troll that lived in a magical knapsack. He preferred rotten food and loved Yahtzee. He played this game with Seth when he was smuggling himself to Wyrmroost, and then many times with Warren when he was wounded, and when he was trapped in the knapsack. Warren developed an attachment to Bubda, and wanted him to leave the bag, but Bubda was to stubborn. Bubda can look like a barrel, or become like elastic.
Eventually (after considerable convincing) the Sorensons talked Bubda into leaving the Knapsack after its connection to the real world was lost, and he resettled in a cell in the Fablehaven dungeon where they made it comfortable for him.