This creature was called a Slavering Grah in this wiki but has been to be a Mucosapedalian Guard-Slime. Treat it with respect.
The name originally chosen for this creature was the Slavering Grah, which was not to be confused with a Slavering Grue. This monster, unlike the Slavering Grue, carries its own light with it (it appears to be slightly luminescent) and attacks adventurers in the dimly lit Clank Hangers beneath The Refuge of Storms. It is seen here after being admonished by Agatha Heterodyne. Notice that it is rather more green than a Slavering Grue, which is somewhere between green and blue.
NOTE: Some refer to this particular monster as a Murgle, which is the noise it makes when walking away confused.
Mucosapedalian Guard Slime Edit
Shown here being confused and looking to Agatha for guidance just before extinguishing the Spark who created it.