Those guys are the definition how to be annoying 😛 They tends to disapear so u got to select every mob to be able to loot him later. Easiest way is to pull his hp bar on the HUD, so u can always select a mob and loot later. Their loot is rly useful.

Dmg type: penetration cold?

Swamp Lurker PrimeSlow12150
Poison Swamp LurkerNormal24250
Ravenous SwamplurkerNormal30350
Mutated SwamplurkerNormal40450
Swamp CreeperNormal1402800

Find this mob on Cyrene Map