New Monster: Scourge Goblin

Here are the stat lines of the scourge goblins.  I'm using Swords & Wizardry for the system.  I'm not a fan of alignment or assigning a single set of stats because I like a range.  In this case I've given you stats for 1HD to 5HD goblins.  Their damage increases by 1 point per HD. 

Scourge Goblins
Hit Dice: 1 to 5 
Armor Class: 5 [14]
Attacks: 2 fists (1d2) and 1 bite (1d3)
Saving Throw: 17 to 12
Special: Immunities
Move: 12
Alignment: Neutral
Number Encountered: 1d4 x 100
Challenge Level/XP: 1/15 to 5/240

Scourge goblins are much like a locus swarm, when a group settles into an area they consume all plant and animal life creating a dead land.  These creatures were created many years ago when the necromancers to the south decided to expand their territories beyond the great river.  The massive goblin tribes were between the undead army and the human kingdoms to the north.  The undead slaughtered all but one tribe who sought assistance from the humans.  The mage-king, Barakus, agreed to aid the goblins by giving them the power to fight the undead.

Barakus's plan succeeded beyond his imagination.  The goblins were now imbued with the immunities against the undead.  They are not paralyzed by a ghouls touch, not drained by a wight nor will they contract a disease by a mummy.  They are immune to the undead's natural abilities.  This immunity does not expand beyond the undead.  A mage casting paralyze has a normal chance of succeeding.  The goblins fought back the undead.  In fact they ate any of the remains they came across.

What occurred afterwards, Barakus has no way of expecting.  The goblins began consuming and multiplying at an alarming rate.  He soon found his kingdom being consumed by his own creation.

Scourge goblins have an extremely high metabolism.   They need food constantly.  They also age and multiply quickly.  The goblin females instead of having one offspring now have a litter of goblins.  A horde of scourge goblins can double in size in one month.

Scourge goblins build very distinct settlements.  There are grouped villages surrounded by a large earthen wall that wraps around miles of area.  They are able to construct these massive walls extremely quick.  Once the wall is completed, they begin devouring the countryside.  It seems the only things they will not eat are the four elements, even water.  They usually stay in one location for two to three months before moving on. A stark dead land marks their path.