Unicycle

The Eleventh Doctor was skilled at riding a unicycle. He once participated in Le Tour de Parisian Dix, a unicycling race on a lava planet, and won the race for the eleventh time. The Doctor joined the race to help a Galactic Marshal catch a dangerous criminal. (COMIC: Le Tour de Death)

The Seventh Doctor and Ace came across a clown on a unicycle at the Psychic Circus. Ace was afraid of clowns. (TV: The Greatest Show in the Galaxy)

The Doctor and Ace later encountered another man, who was juggling several balls while on a unicycle. The man got distracted, and one of the balls hit Ace on the head. (PROSE: One Card for the Curious)