Waterveiled Assassin (CR 15)

Large Elemental (Extraplanar and Water)
Alignment: Always neutral evil
Initiative: +10(+6 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., blindsight 60 ft.;, Listen +20, and Spot +20
Languages: Aquan, Common

AC: 25 (-1 size, +6 Dex, +10 natural), touch 15, flat-footed 19
Hit Dice: 26d8+52 (169 hp); DR: 10/-
Fort +20, Ref +28, Will +21
Speed: 30 ft. and fly 40 ft. (perfect)
Space: 10 ft.; Reach 20 ft.
Base Attack +19; Grapple +30
Attack: Melee slam +26 (4d8+10)
Special Attacks/Actions: churn, engulf
Attack Options: Combat reflexes
Abilities: Str 25, Dex 23, Con 15, Int 10, Wis 16, Cha 12
Special Abilities: Liquid body, SR 23, fast healing 5, malleable form
Special Qualities: Elemental traits:(immune to critical hits, electricity, flanking, paralysis, petrification, poison, sleep effects, sneak attacks, stunning), one with water
Feats: Alertness, Combat Reflexes, Improved Initiative, Lightning Reflexes, Improved Natural Attack (slam), Iron Will, Skill Focus (Hide), Skill Focus (Move Silently), Weapon Focus (slam),
Skills: Hide +19, Listen +20, Move Silently +23, Spot +20, and Swim +15
Advancement: 27-40 HD (Large)
Climate/Terrain: Native to the Elemental Plane of Water
Organization: None
Treasure: Standard

Source: Monster Manual IV

The avatars of Elemental Evil have only recently appeared. Each avatar is the living will of an Prince of Elemental Evil. It contains a tiny fragment of the corresponding prince's essence and exists solely to advance its creator's cause on the Material Plane. The avatars gather at important sites such as recently discovered elemental nodes or other places that might be key to returning the Eye to the world. Sometimes they serve as mighty engines of war for the clerics of the Elder Elemental Eye.

The simmering war between each faction of the Elder Elemental Eye's priests draws in the avatars as well. These creatures are just as likely to turn against each other as they are to ally against a powerful threat.

Liquid Body (Ex): A waterveiled assassin exercises supreme control over its watery form, allowing it to flow around attacks, flatten itself against the ground to avoid a spell's blast, and so forth. Any effect or spell that allows a Reflex save for half damage has a 50% chance to have no effect on a waterveiled assassin.

Malleable Form (Ex): A waterveiled assassin's control over its form allows it to flow through tiny cracks in objects and move through the earth, walls, and other obstacles. The assassin moves at normal speed through terrain that slows movement. It can move through permeable objects at half speed, but it cannot move through completely solid barriers. For example, an assassin could flow through a wooden or brick wall by squeezing into cracks and channels, but it could not move through a wall of solid iron or rock, such as that produced by wall of stone.

If the assassin ends its movement completely within an object, opponents do not have line of sight or line of effect to it. Its reach drops to 0 feet. Any creatures engulfed within the assassin (see Engulf below) fall out, dropping prone at the edge of the object. If only part of the assassin is in an object, but its remaining space cannot hold all the creatures within it, the assassin chooses which ones to release.

Churn (Ex): As a swift action, a waterveiled assassin can create mighty currents within its body that grind engulfed creatures, dealing 5d6 points of bludgeoning damage. An engulfed creature that succeeds on a DC 30 Fortitude save takes half damage. The save DC is Strength-based.

Engulf (Ex): As a standard action, a waterveiled assassin can flow over Medium or smaller creatures, entrapping them within its liquid form. The assassin simply moves into the opponents' space; any creature whose space it completely covers is subject to the engulf attack. The assassin cannot make a slam attack during a round in which it engulfs. It can engulf as many creatures as fit in its space.

Opponents can make attacks of opportunity against the assassin, but if they do so they are not entitled to a saving throw. Those who do not attempt attacks of opportunity must succeed on DC 30 Reflex saves or be engulfed; on a success, a creature moves aside or back (opponent's choice) to move out of the assassin's path. The save DC is Strength-based.

Engulfed creatures are considered to be grappled within the assassin's body, and they are subject to its churn attack (see above). Engulfed creatures that breathe air might drown (DMC 304).

One With Water (Ex): Since a waterveiled assassin's body is liquid, it can simply disappear into water. An assassin in a volume of water at least 15 feet wide, 15 feet long, and 15 feet deep is invisible. It remains invisible as long as it remains within water, even if it attacks.

Skills: A waterveiled assassin has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.

Extraplanar Subtype

A subtype applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. This book assumes that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have when on its home plane). An extraplanar creatures usually has a home plane mentioned in its description. These home planes are taken from the Great Wheel cosmology of the D&D game (see Chapter 5 of the Dungeon Master's Guide). If your campaign uses a different cosmology, you will need to assign different home planes to extraplanar creatures.

Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane; the transitive planes in the D&D cosmology are the Astral Plane, the Ethereal Plane, and the Plane of Shadow.

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.