Grumblegut is a named Volcanic Pustule that can be found either northeast of Dralk (22195,29207) amongst other Volcanic Pustules, or on the Island of Fire amongst the fire beetles. It has also been spotted on the ashen ground southwest of Dralk (21876,28724).
Try to mezz, stun and root and pull him alone to a safe spot. He hits hard for his level.
Grumblegut has a chance to drop the following: