I too remember Eureeka's Castle. I remember watching some episodes during my college days. Yes, the show does remind me a lot of Sesame Street with those familiar voices. I remember.
Eureeka, a wizard in training.
Her adopted dragon, Magellan.
Batly the egotistic bat.
The furry moat twins, Bogge and Quagmire, who love to quarrel.
Mr. Knack who owned a trading wagon.
Kate the reporter mouse,
Emma the rotund hungry mouse.
Sir Clank the old mouse who lives in a suit of armor.
The singing stone fish known as the Fishtones.
Cooey, a fuzzy yellow creature who coos and was Magellan's pet.
Webster, a spider like creature who was Batly's pet.
The clay worms known as the Slurms.
The living blanket dots on Magellen's blanket known as the Blanketeers.
And the nameless giant who loves to wind the key on the castle so it can play them music.