Sandtrap

Sandtraps sit quietly in the desert or in subterranean passages, awaiting their prey. They usually don't attack unless their prey fall for their ambush, unless of course they are particularly hungry. Their corrosive slime allows them to eat through stone, creating the sand needed to hide within.

Huge Aberration
HD: 13d8 + 50 (120 hp)
Initiative: +10
Speed: 15 ft. (3 squares)
Armor Class: 21 (-2 size, +3 Dex, +9 natural), touch 12, flat-footed 16
Base Attack/Grapple: +4/+13
Attack: Slam +12 melee (1d6+5)
Full Attack: Slam +12 melee (1d6+5) and bite +8 melee (3d4+2)
Space/Reach: 15 ft./15 ft. (5 ft. with bite)
Special Attacks: Engulf, Corrosive slime
Special Qualities: Darkvision 60 ft.
Saves: Fort +10, Ref +7, Will +5
Abilities: Str 23, Dex 16, Con 17, Int 14, Wis 15, Cha 11
Skills: Hide +13, Listen +13, Move Silently +12, Spot +8
Feats: Alertness, Combat Reflexes, Improved Initiative
Environment: Underground
Organization: Solitary
Challenge Rating: 9
Treasure: Standard
Alignment: Usually chaotic neutral
Advancement: 14-18 HD (Colossal)
Level Adjustment: —

Engulf: Using sand-coated flaps, a sandtrap can suck a large or smaller creature in its body as a standard action. This does not provoke an attack of opportunity. If it wins a grapple check,, it gains hold of the victim, and can attack with a +4 on the attack roll.

Corrosive Slime: Per round, sandtraps deliver 2d6 acid damage, 4d6 vs. metallic creatures or objects, 8d10 vs. stone. Metallic armor and weapons become useless in their maws.

Sine they eat through stone, they are found in soily subterranean dwellings, rather than in stony passages.