Example Contestants are 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 BFB, instead of being objects, they are 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 purple, lime or cyan.
They appear again in "Let's Raid The Warehouse", but are considerably more crude.
In TPOT, example contestants are once again, faces, but this time they are transparent-looking or has the same color as the background. They also look more flat compared to other faces.
They appear again in "B.F.B. = Back From Beginning", returning to their ball form, but now with arms. They are black with with eyes.
They made their debut appearance in "Cycle of Life".
They made a second appearance in "Insectophobe's Nightmare".
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 differently colored variants.
They returned with their circle design in "B.F.B. = Back From Beginning", but this time with eyes and arms.