Shade
Monster Junkie
That's delightfully icky. I'd say these are Large aberrations. DR 10/slashing or piercing (or maybe just slashing?), acid resistance, acid spittle on a ranged touch (or maybe a breath weapon?).
Perhaps these are to ogres as driders are to drow? A curse on ogres by a vengeful god for some percieved slight?
All of this sounds great. In fact, there is a deity called simply "The Dark God" within the adventure which possibly created them.
Ogre Ability Scores: Str 21, Dex 8, Con 15, Int 6, Wis 10, Cha 7
Giant Slug Ability Scores: Str 26, Dex 8, Con 21, Int -, Wis 10, Cha 7
Giant slug abilities...
Damage reduction 10/slashing or piercing
Acid Bite (Ex): A giant slug's bite deals 1d6 points of acid damage in addition to any other damage it deals. The damage is not doubled on a critical hit.
Acid Spit (Ex): Giant slugs can spit a ball of caustic saliva with a range of 20 feet, as a ranged touch attack. This attack deals 6d6 points of acid damage on a successful hit. Clothing and armor worn by the target of this spit dissolves and becomes useless immediately unless the item succeeds on a DC 21 Reflex save. The save DC is Constitution-based.
Rubbery Form (Ex): The body of a giant slug is very rubbery, allowing it to squeeze through spaces normally too small for its bulk. A giant slug can move through a space 10 feet wide without squeezing. A giant slug can also move through a space 5 feet wide by taking the standard penalties for squeezing.
Skills: A giant slug has a +8 racial bonus on Move Silently checks.