Here’s a monster that came out of the random monster generator.

Armor Class: 19 (s)
Hit Dice: 1+2
No. of Attacks: 1
Damage: 3d6 or disease (see below)
Movement: 60′
No. Appearing: 3d8, Lair 4d8
Save As: Fighter: 2
Morale: 12
Treasure Type: F
XP: 100

These creatures resemble oversized blue snails, roughly 5 feet long and weighing about 166 pounds. They are highly intelligent (Intelligence 20), a cruel joke invented by a high level Magic User who fused aspects of lycanthropes and snails. As such, they can be harmed only by silver or magical weapons, and they spread their impressive numbers through a kind of magical disease or curse.

A sapphire cursecoil attacks either by bludgeoning a foe with its head for 3d6 damage or by spraying forth a foul ichor (once per day). On a roll of 1-2 on 1d6, the victim contracts the curse that slowly transforms him into another cursecoil, progressively turning blue and folding into a snail-like shape until the change is complete. At any time before this end state, the victim may be restored with a remove curse spell. Afterwards, only a restoration spell can reverse it.

Sapphire cursecoils are fearless and cunning, often found in groups that plan ambushes or use their curse to create more of their kind. They glide swiftly on their ventral feet, often swarming unsuspecting victims.

Of course, I had to make some sense of the output, which was as follows.

Armor Class = 19 (s)
Hit Dice = 1 + 2 HD
5 feet, 166 pounds
Attacks = Disease or bludgeon 3d6
Movement = 60
No. Appearing = 3d8, 4d8 in lair
Save As = Fighter
Morale = 12
Treasure Type = F
Curse 1-2 on d6.
Looks like a blue snail.  
Highly intelligent (20 INT)

A party of 4 adventurers of maybe 4th level should have a good time fighting off 15 or so of these guys. With low HD, they likely won’t land many hits, but woe to those victims that do get walloped. With 30 days to reverse the curse, it’s not too bad for PCs. The average 0-level villager has no chance.