You see an empowered glooth horror.
Notes
It is the second "boss" of the Hero of Rathleton Quest. It is the final stage of the Feeble Glooth Horror, which bisects into 16 Empowered Glooth Horrors in total.
Abilities
?.
Damage Taken From Elements
Physical 
Death 
Holy 
Ice 
Fire
Energy
Earth
Location
Behaviour
Fights in close combat. An empowered glooth horror never retreats.
Strategy
If your team isn't strong enough, avoid facing all 16 of them at the same time. Other than that, just kill them quickly using area spells like you did with the other creatures in the room.