Gruzzer

Attacks
Flies around ignoring the player, bumping into walls and objects, changing direction.

Tactics
It is best to follow behind their movement and strike them down. Just keep an eye that they don't bounce back into your direction.

Trivia
On the official website, it is referred to as "Droobling Muzznik":

"These morose-looking flies buzz around haphazardly through the caverns, bouncing off of walls and irritating travellers."