It, like all other enemies/hazards, takes away one pair of pants from SpongeBob's health unit. However, not all clowns are enemies, as some can help SpongeBob by creating challenges with rewards for successful attempts, such as letter tiles.
These enemies seem to work for Plankton, but can sometimes be rebellious and do what they desire. As long as Plankton doesn't wonder what they're up to, they tend to follow through with their mischievous plans. Plankton assigns them tasks such as operating games at Chum World, performing in the big top, and guarding level areas throughout the prementioned amusement park. It seems that Plankton treats his clowns harshly and gives them nasty punishments (or instant dismissal) if they disobey him. It's also apparent that the enemy clowns are merely following orders from Plankton: to attack SpongeBob if they see him. Either that, or they are just thuggish bullies who take pleasure from hurting SpongeBob (the first suggestion is probably more likely).
These enemies can remain stationary, walk inside of a set range in a consistent pattern, or even fire out of cannons. The walking ones are the ones that attack; the others either talk to him or do nothing. If SpongeBob gets close, they stop walking. But if the daring sea sponge gets too close, the wandering circus performers will bite SpongeBob. To defeat these anglerfish fiends, the yellow parazoa must hit it not once, but twice (with one exception).
The chart below shows data about each Chum World Clown.