Ectoplasm Elemental, Large (CR 5)

Large Elemental (Water)
Alignment: Usually neutral
Initiative: +8 (+4 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., Listen +8, and Spot +7

AC: 19 (-1 size, +4 Dex, +6 natural), touch 13, flat-footed 15
Hit Dice: 8d8+24 (60 hp); DR: 5/--
Fort +9, Ref +6, Will +2
Speed: 40 ft., swim 40 ft.
Space: 10 ft./5 ft.
Base Attack +6; Grapple +14
Attack: Slam +10 melee
Full Attack: Slam +10 melee
Damage: Slam 2d6+6 plus 2d6 acid
Special Attacks/Actions: Acid touch, envelop, improved grab
Abilities: Str 19, Dex 19, Con 17, Int 4, Wis 11, Cha 11
Special Qualities: Acid immunity, elemental traits, water subtype
Feats: Alertness; Improved Initiative; Weapon Focus (slam)
Skills: Listen +8 and Spot +7
Advancement: -
Climate/Terrain: Any land and underground
Organization: Solitary
Treasure/Possessions: None

Source: Web

Acid Touch (Ex): Those struck by the ectoplasm elemental must make a Fortitude save (DC 10 + 1/2 elemental's HD) or take acid damage the following round. The amount of damage is the same as the amount added to the slam attack. For example, a Medium ectoplasm elemental would cause 1d6 points of acid damage the round after a successful attack, unless the target made a Fortitude save (DC 12).

Improved Grab (Ex): When the elemental makes a successful melee attack, it can follow up with an immediate grapple attempt. If this grapple is successful, the elemental can attempt to envelop the target.

Envelop (Ex): If the elemental makes a successful grapple, it can attempt to envelop the target. The target must make a Reflex save (DC 10 + 1/2 elemental's HD) or it gets drawn into the body of the elemental. The victim of this attack cannot free itself through physical means. Each round while trapped in this manner, the victim takes the same acid damage as the elemental causes with its acid touch. An ectoplasm elemental can envelop only 1 target that is one size smaller than itself, or up to 2 targets two sizes smaller than itself. For example, a Large ectoplasm elemental can envelop 1 Medium target, or 2 Small targets.

Damage Reduction: As the elemental grows in size, it gains the damage reduction listed.

Ectoplasm elementals tend to ignore most things, but they are quick to attack if provoked. They grapple and envelop the closest opponent.

Water Subtype

This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane of Water. Creatures with the water subtype always have swim speeds and can move in water without making Swim checks. A water creature can breathe underwater and usually can breathe air as well.