Mokey slaps the Gagtoothed Groan
The Gagtoothed Groan is featured in the Fraggle Rock book Best Friends. He lives deep inside the Den of the Gagtoothed Groan, where Mokey and Red have traveled to get a new Brushplant for Mokey's painting of Red. Red traveled with Mokey to protect her from the Groan, but it is Red who gets captured by the Groan, and saved by Mokey.
The Groan also appears, with a different design, in Fraggle Countdown.