The Interdimensional Creature is an alien monster from another realm, resembling a green, fish-like creature capable of human speech.
He was accidentally summoned by Uncle in an attempt to find Jackie, who had been shrunken down to a tiny size because of a spell gone awry. The Creature thanked the Chans for freeing him, but when Tohru offered him cookies, he tried to eat Jade instead. Fortunately, Uncle quickly banished the Creature back to his home dimension before he could devour the young girl.