Frumpkin

Frumpkin is the familiar of Caleb Widogast. Caleb usually summons him in the form of an orange tabby cat. As a companion, he is controlled by his summoner, Liam O'Brien, with assistance and communication from the Dungeon Master, Matthew Mercer.

As a familiar, Frumpkin can appear, disappear, and/or reappear at Caleb's whim (requires one action). Caleb can issue telepathic commands to Frumpkin. Caleb can transfer his senses to Frumpkin, though this renders Caleb's body temporarily blind and deaf.

Recalling a previous adventure, Frumpkin had taken the form of an octopus and was used as a cushion to break Nott's fall out of a burning building.

When Frumpkin loses all hit points or when Caleb wants to change Frumpkin's form, Caleb can cast Find Familiar again to bring Frumpkin back or change his form.

Forms
Although Frumpkin's base form was that of a Cat, through the find familiar spell Caleb could change his form into various creatures including that of a:
 * Sparrow
 * Octopus
 * Peregrine Falcon
 * Owl

Trivia

 * Liam shared his vision of Frumpkin on Instagram (source).
 * Frumpkin disappeared in due to a gnoll attack reducing his bird form's hit points to zero.   marked Frumpkin's first full episode absence.  In the episode following this absence, Caleb resummoned Frumpkin in his cat form. Frumpkin was kicked by a guardsman while trying to get into the Spires and his hit points were once again reduced to zero.
 * Caleb has stated that Frumpkin is never upset over his deaths and has a good sense of humor when it comes to them.