Clowns have minor roles in the Soul Eater Universe, but two in it are legible to use for roleplaying and count as Enhancements for a Witch*.

The Black Clown

The Black Clown is, which is quite explanatory, a black clown. This Clown, an entity of Black Blood, has the ability to fuse with people and create new, more powerful beings. It can also fuse with attacks to increase their its power.
300px-The Man-made Clown

The Black Clown in it's regular form

The Purple-Dyed Clown

The Purple-Dyed Clown is a manifest of clownish ideals with only a mouth and a crescent-shaped, striped body. This Clown, a pure manifestation accidentally created, has the ability to defend and block oncoming attacks from anything.
300px-The Purple-Dyed Clown

The Purple-Dyed Clown in it's generic form

*These clowns can only be used as Enhancements if you have at least one Witch, as only a Witch can use these.