The nightmare chicken is an imaginary character who appears in Uma's dreams.
The chicken appears in the episode "Uma Dreams!" as a figment of Uma's imagination. It is first seen in Uma's nightmare as a gigantic, scary silhouette that she can't identify and mistakes for a monster. It starts to walk toward her as a loud stomping sound plays. Uma is stricken with fear and wakes up before it reveals itself.
When Uma falls back asleep, she finds a magical chain that turns her nightmare into a brightly-lit sunrise scene. The "monster" becomes her favorite animal: a chicken. Uma and the chicken dance together until morning comes. When Uma wakes up, she runs downstairs and reenacts the chicken dance from her dream.
The chicken was played by Tim Lagasse.
It is a fair-skinned hand puppet. It has a tall red comb and dark brown eyes similar to Oobi's. Four fingers act as its upper beak, while its thumb acts as its lower beak.