Example Contestants are Yellow Faces (previously armless silhouettes that resemble Golf Ball) that show off how challenges are supposed to be played out, and sometimes used to show some other non-challenge related things.
In BFDI, they were green or white armless balls with no features that had a strong resemblance to Golf Ball. They were first seen in "Cycle of Life" to show off the challenge.
In BFB, instead of being objects, are Yellow Faces, but are noticably more expressive and have more movements. They are typically yellow, but as seen in "What Do You Think of Roleplay?", they can be green or cyan.
They made their debut appearance in "Cycle of Life".
They made their return as Yellow Faces starting in "Four Goes Too Far".
They were seen again in "What Do You Think of Roleplay?", with different colored variants.