Cerberus has two shepherd (or more likely, doberman) heads (one brown and one red) and one poodle head, (it is believed that the poodle is a girl and the shepherds are boys because the poodle didn’t completely fall for Little Delicious like the other two did). Cerberus’s three heads all have different personalities. Cerberus can breathe and urinate flames. A special whistle can be used to call Cerberus from where ever he is, and when this whistle is blown, Cerberus appeared in the form of a comet with a tail.
Cerberus married Little Delicious, a small Chihuahua that was owned by Mindy at the time. Together, Cerberus and Little Deliciouse had a puppy that was found by Billy, a three-headed demon Chihuahua that he named "Little Chiba".
Cerberus makes another appearance later in the series, playing 'fetch' with Grim and Billy, with Grim sending Cerberus' toy ball flying by hitting it with his scythe. Cerberus has seemed to have become more tame since his encounter with Mandy.
Cerberus also makes an appearance during the opening credits of Billy and Mandy's Big Boogey Adventure, when he appears to have three heads that are all the same, accompanied by the lyrics; "Cerberus, my lapdog, as loyal as can be".