The Playbackyderms is a Monster family consisting of three Monsters that are very similar in their instruments and use of symbiotic partners in playing: Woolabee, Peckidna, and Cherubble. The official name of this Monster family was first revealed in Cherubble's bio. Its existence was first hinted at in Peckidna's bio, which noted similarities between it and Woolabee.
The family's name is a portmanteau of "play", "back", and "pachyderm", a name for a member of the obsolete order Pachydermata, which includes elephants.
The family has a convoluted history. Despite Peckidna's bio stating that it and Woolabee evolved independently from one another, Cherubble's bio states that it is a common ancestor to both. This contradiction was corrected in Epic Cherubble's bio, which clarifies that Cherubble served as an inspiration for Woolabee and Peckidna, rather than being their biological ancestor.
So in short, Cherubble was the first Playbackyderm. It inspired the Colossals to create Woolabee, and later inspired Stair Shaper to create Peckidna. Woolabee and Peckidna therefore aren't biologically related, but instead 'derivative drafts' of the same Monster.
The Playbackyderms is currently the only family with more than two lines of members where one member (Peckidna) didn't receive any variants after two other members already got their epic variants.