Brain's dog

An unknown dog is seen with The Brain occasionally, appearing in a title card and the Season 3 episode, And Now Let's Talk to Some Kids in the episode-within-an-episode Brain's New Puppy. Most likely this dog does not actually exist but is a figment of the Brain's imagination. If he is real, he could possibly be one of Pal's siblings.

Appearance
This dog looks a lot like Pal but has slightly darker-colored fur.