Paizo appears to have adopted cloakers as a substitute for the closed-content ixitxachitl, which seems a decent enough re-purposing. For the Pathfinder game, Paizo subtly cleaned up the shadow shift ability and changed it to a free action, which is an idea well worth back-porting to 3.5e. As most combats only last only four rounds or so, monsters with many special abilities rarely get a chance to show them all off.
The inspiration for the cloaker is unclear, but it resembles some monsters from one of my favorite Fafhrd and the Gray Mouser stories, “The Sunken Land” (1942), which is in Swords Against Death. In this story, the Mouser glimpses a band of northmen being overwhelmed by black, cloak-like creatures. It's a great case of "less is more," as the terse, ambiguous description of the situation leaves much to the reader's imagination.
It is somewhat challenging in 3.5e to create advanced cloakers, despite their intelligence and array of special abilities—or perhaps it is more accurate to say because of these very traits. The cloaker special abilities are a bit of a hodgepodge, muddying the monster's role, and none scale well with additional hit dice or class levels. The aberration creature type is fairly weak, so advancing cloakers by HD does relatively little beyond increasing their size to Huge. Cloakers could certainly take levels in character classes, but many classes would be considered non-associated and thus have limited effect on the final challenge rating. In 2e or 5e, where monster design is far looser, one could just create a "master cloaker" with some new abilities. In 3.5e, a species-specific prestige class might be the best way to go, a class that enhanced and maybe expanded the moan and shadow shift abilities.
The following text is Open Game Content.
This shape, like a great black cloak, ripples and rises up into the air, opening up into a billowing sheet of darkness.
A Strange, Alien Race. The cloakers are most often found in the deep underground realms, where they are feared and avoided by the other races. The goals and motivations of the cloakers are largely unknown.
Deceptive Appearance. When resting or lying in wait, these creatures are almost impossible to distinguish from common black cloaks (the cloaker’s ivory claws look very much like bone clasps). Only when it unfurls does the horrific nature of the creature become apparent.
Weird and Unsettling Abilities. Cloakers emit an eerie moaning that can induce baleful effects in the listener. They are able to manipulate shadows to produce spell-like effects.
A cloaker has a wingspan of about 8 feet. It weighs about 100 pounds.
Cloaker CR 5
Usually CN Large aberration
Init +7; Senses darkvision 60 ft.; Listen +13, Spot +13
Languages Undercommon
Defense
AC 19, touch 12, flat-footed 16
(+3 Dex, +7 natural, -1 size)
hp 45 (6d8+18 HD)
Fort +5, Ref +5, Will +7
Special Defenses shadow shift
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +8 (1d6+5), bite +3 (1d4+2)
Space 10 ft.; Reach 10 ft. (5 ft. with bite)
Special Attacks engulf, moan
Tactics
Before Combat Cloakers usually lie still, watching and listening for prey.
During Combat If facing a single opponent, a cloaker uses its engulf attack. Against multiple foes, it lashes with its tail in concert with its moan and shadow shift abilities to reduce the opposition’s numbers, then engulfs a survivor. Multiple cloakers usually split up, leaving one or two behind to use special abilities while the rest make melee attacks.
Morale Individual cloakers fight until brought to 20 hp or less; groups of cloakers retreat once half their number are slain.
Statistics
Str 21, Dex 16, Con 17, Int 14, Wis 15, Cha 15
Base Atk +4; Grp +13
Feats Alertness, Combat Reflexes, Improved Initiative
Skills Hide +8, Listen +13, Move Silently +12, Spot +13
Ecology
Environment underground
Organization solitary, mob (3–6), or flock (7–12)
Treasure standard
Advancement 7–9 HD (Large); 10–18 HD (Huge)
Special Abilities
Engulf (Ex) A cloaker can try to wrap a Medium or smaller creature in its body as a standard action. The cloaker attempts a grapple that does not provoke an attack of opportunity. If it wins the grapple check, it establishes a hold and bites the engulfed victim with a +4 bonus on its attack roll. It can still use its whiplike tail to strike at other targets. Attacks that hit an engulfing cloaker deal half their damage to the monster and half to the trapped victim.
Moan (Ex) A cloaker can emit a dangerous subsonic moan as a standard action. By changing the frequency, the cloaker can cause one of four effects. Cloakers are immune to these sonic, mind-affecting attacks. Unless otherwise specified, a creature that successfully saves against one of these effects cannot be affected by the same moan effect from the same cloaker for 24 hours. All save DCs for moan effects are Charisma-based.
Fear: Anyone within a 30-foot spread must succeed on a DC 15 Will save or become panicked for 2 rounds.
Nausea: Anyone in a 30-foot cone must succeed on a DC 15 Fortitude save or be overcome by nausea and weakness. Affected characters fall prone and become nauseated for 1d4+1 rounds.
Stupor: A single creature within 30 feet of the cloaker must succeed on a DC 15 Fortitude save or be affected as though by a hold monster spell for 5 rounds. Even after a successful save, the creature must repeat the save if the cloaker uses this effect again.
Unnerve: Anyone within a 60-foot spread automatically takes a -2 penalty on attack and damage rolls. Those forced to hear the moan for more than 6 consecutive rounds must succeed on a DC 15 Will save or enter a trance, unable to attack or defend themselves until the moaning stops.
Shadow Shift (Su) When in dim illumination, a cloaker can manipulate shadows as a free action to create one of three effects: blur (lasts 1d4 rounds, self only), mirror image (CL 6th), or silent image (DC 15, CL 6th, save DC is Charisma-based).
Variant Cloakers
While most cloakers have a fairly uniform appearance, there are several varieties that stand out from the norm.
Shadowbrood: Believed to be cloakers infused with the energy of the Plane of Shadow, these midnight-black cloakers are often mistaken for incorporeal undead. They can use their shadow shift ability to produce effects identical to darkness and dimension door (self only). Once per day they may use maze and shadow walk as spell-like abilities (caster level 8th). (CR +1)
Vampiric: These yellow-gray cloakers thrive on blood and attach themselves to their prey like leeches. Despite the name, most vampiric cloakers are not undead; however, explorers have reported vampiric cloakers that recoil from holy symbols and are damaged by water, so presumably they somehow can become true vampires, though the mechanics for this are unknown. In addition to the normal powers of cloakers, they have the following abilities. (CR +1)
Attach (Ex): If a vampiric cloaker hits with a bite attack, it uses its powerful jaws to latch onto the opponent’s body and automatically deals bite damage each round it remains attached. An attached cloaker loses its Dexterity bonus to Armor Class and has an AC of 16. An attached cloaker can be struck with a weapon or grappled itself. To remove an attached cloaker through grappling, the opponent must achieve a pin against the creature. A vampiric cloaker can use this ability while it engulfs an opponent.
Blood Drain (Ex): A vampiric cloaker drains blood, dealing 1d4 points of Constitution damage in any round when it begins its turn attached to a victim. Once it has dealt 10 points of Constitution damage, it detaches and flies off to digest the meal. If its victim dies before the cloaker’s appetite has been sated, the cloaker detaches and seeks a new target.
Advanced Cloakers
Cloaker guards are older, larger individuals assigned to protect important cloaker areas.
Cloaker Guard CR 7
Advanced cloaker
CN Huge aberration
Init +6; Senses darkvision 60 ft.; Listen +17, Spot +17
Languages Undercommon
Defense
AC 20, touch 10, flat-footed 18
(+2 Dex, +10 natural, -2 size)
hp 126 (12d8+72 HD)
Fort +10, Ref +6, Will +10
Special Defenses shadow shift
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +17 (2d6+10), bite +12 (1d6+5)
Space 15 ft.; Reach 15 ft. (10 ft. with bite)
Special Attacks engulf, moan
Statistics
Str 30, Dex 14, Con 22, Int 14, Wis 15, Cha 15
Base Atk +9; Grp +27
Feats Ability Focus (moan), Combat Reflexes, Flyby Attack, Improved Initiative, Improved Natural Attack (tail slap)
Skills Hide +9, Listen +17, Move Silently +17, Spot +17
Special Abilities
Moan (Ex) The DC for all effects is 20.
Shadow Shift (Su) DC 18 Will for silent image.
Lurking cloakers wait patiently in the darkness, seeking to catch and destroy stragglers.
Lurking Cloaker CR 8
Cloaker rogue 3
CN Large aberration
Init +10; Senses darkvision 60 ft.; Listen +13, Spot +13
Languages Undercommon
Defense
AC 23, touch 16, flat-footed 17
(+1 deflection, +6 Dex, +7 natural, -1 size)
hp 68 (6d8+18 plus 3d6+18 HD)
Fort +8, Ref +8, Will +8
Special Defenses evasion, shadow shift, trap sense +1
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +11 (1d6+6), bite +6 (1d4+3)
Space 10 ft.; Reach 10 ft. (5 ft. with bite)
Special Attacks engulf, moan, sneak attack +2d6
Statistics
Str 23, Dex 22, Con 17, Int 12, Wis 16, Cha 14
Base Atk +6; Grp +16
Feats Combat Reflexes, Dodge, Great Fortitude, Improved Initiative
Skills Hide +12, Listen +13, Move Silently +16, Search +5, Sense Motive +7, Spot +13, Use Magic Device +8
SQ trapfinding
Combat Gear oil of magic vestment +5, potion of greater magic fang +5, potion of resist energy (fire) 30; Other Gear ring of protection +1
Special Abilities
Moan (Ex) The DC for all effects is 15.
Shadow Shift (Su) DC 15 Will for silent image.
The mind of a cloaker is bizarre, and these creatures do not worship conventional gods, instead choosing to venerate aloof, extra-dimensional beings of mind-shattering power.
Cloaker Suppliant CR 9
Cloaker cleric 7
CN Large aberration
Init +8; Senses darkvision 60 ft.; Listen +12, Spot +12
Languages Undercommon
Defense
AC 22, touch 14, flat-footed 18
(+1 deflection, +4 Dex, +8 natural, -1 size)
hp 140 (6d8+36 plus 7d8+42 HD)
Fort +13, Ref +10, Will +13
Special Defenses shadow shift
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +12 (1d6+4), bite +7 (1d4+2)
Space 10 ft.; Reach 10 ft. (5 ft. with bite)
Special Attacks engulf, moan, rebuke undead 7/day (+4, 2d6+11 HD, 7th)
Spells Prepared (CL 7th, 8th for Chaos spells)
4th—chaos hammer *D (DC 20), inflict critical wounds (+12 melee touch, DC 20), spell immunity
3rd—bestow curse (+12 melee touch, DC 19), deeper darkness, prayer, rage D (DC 19)
2nd—death knell (DC 18), hold person (DC 18), inflict moderate wounds (+12 melee touch, DC 18), resist energy, shatter (DC 18), touch of madness D (+12 melee touch, DC 18)
1st—bane (DC 17), cause fear (DC 17), command (DC 17), detect law *, doom (DC 17), entropic shield, lesser confusion D (DC 17)
0—detect magic (2), guidance (2), read magic, resistance (2)
D Domain spell, * chaos spell; Domains chaos, madness
Statistics
Str 18, Dex 18, Con 22, Int 14, Wis 20, Cha 18
Base Atk +9; Grp +17
Feats Ability Focus (moan), Combat Casting, Improved Initiative, Improved Natural Armor, Lightning Reflexes
Skills Concentration +16 (+20 casting defensively), Hide +9, Knowledge (arcana) +9, Knowledge (the planes) +9, Listen +12, Move Silently +13, Spellcraft +8, Spot +12, Survival +3 (+5 on other planes)
SQ spontaneous casting (inflict spells)
Combat Gear scroll of greater dispel magic and harm, wand of shatter (30 charges); Other Gear amulet of health +2, ring of protection +1
Special Abilities
Madness Domain For spellcasting (determining bonus spells and DCs), the cloaker suppliant uses its Wisdom score +3 (23) in place of Wisdom alone. For all other purposes, such as skills and saves, the cloaker suppliant uses its Wisdom score -3 (17) in place of Wisdom. (These modifiers are already included in the statistics block.) Once per day, the cloaker suppliant can see and act with the clarity of true madness. The suppliant gains a +3 bonus on a single roll involving Wisdom. The suppliant must choose to use this power before the roll is made.
Moan (Ex) The save DC for all effects is 19.
Shadow Shift (Su) DC 17 Will for silent image.
Vampiric cloakers are revered and feared by other cloakers as being marked with a special power.
Vampiric Cloaker CR 10
Vampiric cloaker fighter 4
CE Large aberration
Init +8; Senses darkvision 60 ft.; Listen +14, Spot +14
Languages Undercommon
Defense
AC 23, touch 14, flat-footed 19
(+1 deflection, +4 Dex, +9 natural, -1 size)
hp 102 (6d8+30 plus 4d10+20)
Fort +11, Ref +7, Will +9
Special Defenses shadow shift
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +15 (1d6+8), bite +11 (1d6+6/19-20)
Space 10 ft.; Reach 10 ft. (5 ft. with bite)
Special Attacks attach, blood drain, engulf, moan
Statistics
Str 26, Dex 19, Con 20, Int 14, Wis 16, Cha 12
Base Atk +8; Grp +20
Feats Combat Expertise, Improved Critical (bite), Improved Initiative, Improved Natural Attack (bite), Improved Trip, Weapon Specialization (bite), Weapon Focus (bite)
Skills Hide +11, Listen +14, Move Silently +15, Spot +14
Gear amulet of natural armor +2, ring of protection +1
Special Abilities
Attach (Ex) If a vampiric cloaker hits with a bite attack, it uses its powerful jaws to latch onto the opponent’s body and automatically deals bite damage each round it remains attached. An attached cloaker loses its Dexterity bonus to Armor Class and has an AC of 16. An attached cloaker can be struck with a weapon or grappled itself. To remove an attached cloaker through grappling, the opponent must achieve a pin against the creature. A vampiric cloaker can use this ability while it engulfs an opponent.
Blood Drain (Ex) A vampiric cloaker drains blood, dealing 1d4 points of Constitution damage in any round when it begins its turn attached to a victim. Once it has dealt 10 points of Constitution damage, it detaches and flies off to digest the meal. If its victim dies before the cloaker’s appetite has been sated, the cloaker detaches and seeks a new target.
Moan (Ex) The DC for all effects is 14.
Shadow Shift (Su) DC 14 Will for silent image.
Elder cloakers are some of the largest and oldest cloakers known, generally found only in the deepest and darkest parts of the earth and occasionally on the Plane of Shadow.
Elder Cloaker CR 12
Advanced elite shadowbrood cloaker
Usually CN Huge aberration
Init +7; Senses darkvision 60 ft.; Listen +22, Spot +22
Languages Undercommon
Defense
AC 21, touch 11, flat-footed 18
(+3 Dex, +10 natural, -2 size)
hp 228 (18d8+144 HD)
Fort +14, Ref +9, Will +12
Special Defenses shadow shift
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +22 (2d6+11), bite +17 (1d6+5)
Space 15 ft.; Reach 15 ft. (10 ft. with bite)
Special Attacks engulf, moan
Spell-Like Abilities (CL 8th)
Statistics
Str 32, Dex 17, Con 26, Int 14, Wis 12, Cha 18
Base Atk +13; Grp +32
Feats Ability Focus (moan), Combat Reflexes, Dodge, Flyby Attack, Improved Flyby Attack, Improved Initiative, Improved Natural Attack (tail slap)
Skills Hide +16, Listen +22, Move Silently +24, Spot +22
Special Abilities
Moan (Ex) The DC for all effects is 25.
Shadow Shift (Su) When in dim illumination, an elder cloaker can manipulate shadows as a free action to create one of five effects: blur (lasts 1d4 rounds, self only), darkness (CL 6th), dimension door (self only, up to 640 ft.), mirror image (CL 6th), silent image (DC 23, CL 6th).
Cloaker Shadow Weavers use arcane magic to tap into the mysterious power of the Plane of Shadow.
Cloaker Shadow Weaver CR 13
Cloaker sorcerer 11
CN Large aberration
Init +9; Senses darkvision 60 ft.; Listen +14, Spot +14
Languages Undercommon
Defense
AC 26, touch 17, flat-footed 21
(+3 deflection, +5 Dex, +9 natural, -1 size)
hp 143 (6d8+30 plus 11d4+55 HD)
Fort +8, Ref +8, Will +14
Special Defenses shadow shift
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +12 (1d6+4), bite +7 (1d4+2)
Space 10 ft.; Reach 10 ft. (5 ft. with bite)
Special Attacks engulf, moan
Spells Known (CL 11th)
5th (5/day)—shadow evocation (DC 22), waves of fatigue
4th (7/day)—crushing despair (DC 19), enervation (+13 ranged touch), shadow conjuration (DC 21)
3rd (7/day)—dispel magic, lightning bolt (DC 18), ray of exhaustion (+13 ranged touch, DC 18), slow (DC 18)
2nd (7/day)—blindness/deafness (DC 17), darkness, scare (DC 17), touch of idiocy (+12 melee touch)
1st (8/day)—disguise self, mage armor, ray of enfeeblement (+13 ranged touch), shield, shocking grasp (+12 melee touch)
0 (6/day)—daze (DC 15), detect magic, ghost sound (DC 17), mage hand, ray of frost (+13 ranged touch), prestidigitation, read magic, resistance, touch of fatigue (+12 melee touch, DC 15)
Statistics
Str 18, Dex 20, Con 20, Int 14, Wis 16, Cha 21
Base Atk +9; Grp +17
Feats Alertness, Eschew Materials, Greater Spell Focus (illusion), Improved Initiative, Spell Focus (illusion), Still Spell
Skills Concentration +19, Hide +11, Knowledge (arcana) +16, Listen +14, Move Silently +14, Spellcraft +18, Spot +14
SQ summon familiar
Combat Gear scroll of deep slumber and suggestion, wand of major image (30 charges); Other Gear amulet of natural armor +2, ring of protection +3
Special Abilities
Moan (Ex) The DC for all effects is 18.
Shadow Shift (Su) DC 18 Will for silent image.
Shadow Lord cloakers are often the rulers of large cloaker communities deep beneath the earth.
Shadow Lord Cloaker CR 15
Advanced cloaker shadowdancer 10
CN Large aberration
Init +6; Senses darkvision 60 ft.; Listen +23, Spot +23
Languages Undercommon
Defense
AC 25, touch 18, flat-footed 19
(+3 deflection, +6 Dex, +7 natural, -1 size)
hp 148 (7d8+28 plus 10d8+40 HD)
Fort +9, Ref +15, Will +11
Special Defenses defensive roll, improved evasion, improved uncanny dodge, shadow shift, slippery mind; Resist fire 10
Offense
Spd 10 ft., fly 40 ft. (average)
Melee tail slap +18 (1d8+4), bite +12 (1d4+2)
Space 10 ft.; Reach 10 ft. (5 ft. with bite)
Special Attacks engulf, moan, shadow illusion
Statistics
Str 19, Dex 22, Con 18, Int 18, Wis 16, Cha 18
Base Atk +12; Grp +20
Feats Combat Reflexes, Dodge, Flyby Attack, Improved Natural Attack (tail slap), Weapon Finesse, Weapon Focus (tail slap)
Skills Bluff +14, Decipher Script +14, Diplomacy +6, Disguise +14 (+16 acting), Escape Artist +16, Hide +22, Intimidate +6, Listen +23, Move Silently +26, Perform (dance) +19, Search +19, Sleight of Hand +8, Spot +23, Survival +3 (+5 to follow tracks), Use Rope +6 (+8 to bind)
SQ hide in plain sight, summon shadow, shadow jump 160 ft.
Combat Gear eyes of doom; Other Gear amulet of health +2, minor ring of energy resistance (fire), ring of protection +3
Special Abilities
Defensive Roll (Ex) Once per day, when a shadow lord cloaker would be reduced to 0 hit points or less by damage in combat (from a weapon or other blow, not a spell or special ability), it can attempt to roll with the damage. It makes a Reflex saving throw (DC = damage dealt) and, if successful, takes only half damage from the blow. It must be aware of the attack and able to react to it in order to execute its defensive roll. If it is in a situation that would deny it any Dexterity bonus to AC, it can’t attempt a defensive roll.
Hide in Plain Sight (Su) A shadow lord cloaker can use the Hide skill even while being observed. As long as it is within 10 feet of some sort of shadow, it can hide itself from view in the open without anything to actually hide behind. It cannot, however, hide in its own shadow.
Improved Evasion (Ex) If a shadow lord cloaker makes a successful Reflex saving throw against an attack that normally deals half damage on a successful save, it instead takes no damage. A shadow lord cloaker takes only half damage even if it fails its saving throw. A helpless shadow lord cloaker does not gain the benefit of improved evasion.
Improved Uncanny Dodge (Ex) A shadow lord cloaker retains its Dexterity bonus to AC regardless of being caught flat-footed or struck by an invisible attacker. A shadow lord cloaker cannot be flanked except by a rogue of 14th or higher level. (It still loses any Dexterity bonus to AC if immobilized.)
Moan (Ex) The DC for all effects is 17.
Shadow Illusion (Sp) A shadow lord cloaker can create visual illusions. This ability’s effect is identical to that of the arcane spell silent image and may be employed once per day.
Shadow Jump (Su) A shadow lord cloaker can travel between shadows as if by means of a dimension door spell. The limitation is that the magical transport must begin and end in an area with at least some shadow. This amount can be split among many jumps, but each one, no matter how small, counts as a 10-foot increment.
Shadow Shift (Su) DC 17 Will for silent image.
Slippery Mind (Ex) If the shadow lord cloaker is affected by an enchantment and fails its saving throw, 1 round later it can attempt its saving throw again. It only gets this one extra chance to succeed at its saving throw. If it fails as well, the spell’s effects occur normally.
Summon Shadow (Su) A shadow lord cloaker can summon a 7 HD shadow, an undead shade. Unlike a normal shadow, this shadow’s alignment matches that of the shadow lord cloaker, and the creature cannot create spawn. The summoned shadow cannot be turned, rebuked, or commanded by any third party. This shadow serves as a companion to the shadow lord cloaker and can communicate intelligibly with the shadow lord cloaker.