You see The Blightfather.
Notes
It is the Lancer Beetles' boss that spawns with their raid in Muggy Plains (30 minutes after the initial raid message).
Abilities
Melee (?)
makes you Cursed (damage raises up to ?)
Poison Bomb around itself
Summons (1-2 Lancer Beetle)Damage Taken From Elements
Physical 
Death
Holy
Ice
Fire
Energy
Earth
Drown
Location
Behaviour
The Blightfather will retreat at 4 to 24 (1% - 6%, deep red to red) health.
Strategy
Simply kill it. The Blightfather is as strong as an ordinary Lancer Beetle, just faster.