Gelatinous Cube (CR 3)

Large Ooze
Alignment: Always neutral
Initiative: -5 (Dex); Senses: blindsight

AC: 4 (-1 size, -5 Dex), touch 4, flat-footed 9
Hit Dice: 4d10+32 (54 hp)
Fort +9, Ref -4, Will -4
Speed: 15 ft.
Space: 10 ft./5 ft.
Base Attack +3; Grapple +7
Attack: Slam +2 melee (1d6 and 1d6 acid)
Special Attacks/Actions: Engulf, paralysis, acid
Abilities: Str 10, Dex 1, Con 26, Int -, Wis 1, Cha 1
Special Qualities: transparent, electricity immunity, ooze traits
Feats: -
Skills: -
Advancement: 5-12 HD (Large); 13-24 HD (Huge)
Climate/Terrain: Any underground
Organization: Solitary
Treasure/Possessions: 1/10th coins; 50% goods (no nonmetal or nonstone); 50% items (no nonmetal or nonstone)

Source: Monster Manual

Engulf (Ex): Although it moves slowly a gelatinous cube can simply mow down Large or smaller creatures as a standard action. It cannot make a slam attack during a round in which it engulfs.

The gelatinous cube merely has to move over the opponent, affecting as many as it can cover. Opponents can make opportunity attacks against the cube, but if they do so they are not entitled to a saving throw. Those who do not attempt opportunity attacks must succeed at a Reflex save (DC 13) or be engulfed; on a success, they are pushed back or aside (opponent's choice) as the cube moves forward. Engulfed creatures are subject to the cube's paralysis and acid, and are considered to be grappled and trapped within its body.

Paralysis (Ex): Gelatinous cubes secrete an anesthetizing slime. A target hit by a cube's melee or engulf attack must succeed at a Fortitude save (DC 16) or be paralyzed for 3d6 rounds. The cube can automatically engulf a paralyzed opponent.

Acid (Ex): A gelatinous cube's acid does not harm metal or stone.

Transparent (Ex): Gelatinous cubes are hard to see, even under ideal conditions, and it takes a successful Spot check 15) to notice one. Creatures who fail to notice a cube and walk into it are automatically engulfed.

Blindsight (Ex): An ooze's entire body is a primitive sense organ that can ascertain prey by scent and vibration within 60 feet.

Oozes attack any creatures they encounter.

A gelatinous cube attacks by slamming its body into its prey. It is capable of lashing out with a pseudopod, but usually engulfs foes.