Bone is an original (and extremely minor) character in the comic, first appearing alongside his master in Episode 0071. He is completely imaginary, being a figment of The Guardian's mind, and cannot be seen by anyone except the Guardian, Kumera's magic camera, the readers, and possibly Xande. It is of a completely made-up species and is called a Florgle. He is incapable of making sound, except when speaking to the Guardian, in which case, he'll silently whisper into his ear.
Bone appears to be a white ball of fluff, with tiny limbs, white angel wings, and a purple pompom on an antenna. His eyes are blue, and he has no visible mouth (it is obscured by fur).
Bone can only communicate its thoughts through expressions and body language, and is largely implied to agree with anything the Guardian says or does, though still gets confused when his master starts one of his rants.