Mookie is a purple anthropomorphic mouse with pink inner ears, four to five strands of hair on each side of his head, and a long purple tail. He dons a red baseball cap displaying a yellow and black logo with the number "3," along with white cartoon gloves, silver eyes, a black nose, and two visible toes.

Obsessively fixated on the number three as a source of luck, he structures his life around it, a habit that sometimes annoys fellow characters. Hyperactive, caring, and humorous by nature, he frequently displays clumsiness. His hobbies include active participation in fishing and baseball alongside others.

As Baby Felix’s closest friend, Mookie regularly embarks on adventures and problem-solving missions with him. Their bond drives numerous episodes, such as outdoor trips where Mookie showcases fishing expertise or faces competitions. In one instance, he tumbles into a lake and gets rescued by Baby Felix using a magic bag.

Mookie consistently engages in group activities like camping or baseball games, propelling episodic plots through collaborative tasks or moments requiring aid. His background remains unexplored in documented materials.