Wikia

Fungalmancer Glop is the leader of the stone troggs at Verlok Stand, found with his mushrooms deep within the Fungal Deep^{[68.6, 29]} nearby. His magic is responsible for the disease spreading amongst the Fungal Behemoths.

Objective of

Item	Source	Use
[Embersilk Cloth]	Drop	[Tailoring] [First Aid] [Engineering]
[Flame-Scarred Junkbox]	[Pick Pocket]	To open
[Rogue's Draught]	[Pick Pocket]	Rogue consumable

Glop can only be engaged (and, therefore, looted/pick pocketed) when players are on the aforementioned quests.
Glop is immune to snares and stuns.
Technically every time players encounter Glop on the daily quest he is actually the son of the Glop players previously killed.

Glop can't be engaged until after Earthmender Norsala walks down and talks to him. If you have a DoT or some kind of AoE over time, you could try to time it so Glop will take some damage before running off.
Rogues with daggers can use sprint to keep up a bit and [Backstab] Glop while he is running.

Fungalmancer Glop is performed by voice actor Dino Andrade who also provides the voices for Mimiron, Professor Putricide, Mekkatorque and The Death Knight Gnomes. He is also noted for being the voice of The Scarecrow in Batman: Arkham Asylum.