Regulus

This serpent slides forward smoothly, its head raised above the ground. A cluster of horns and crests growing from its brow suggests a crown. Its gazes at you with a self-satisfied expression.

Taken from Creature Codex

The regulus is a proud and haughty creature, and its intensely deadly nature justifies its arrogance. Rare to the point of being almost mythical, tales of the reguli often intermingle freely with those about basilisks and cockatrices, as all three of the creatures have abilities that can bring swift death. The regulus, however, kills with poison and negative energy, not via petrification, and is capable of wiping out entire villages in its toxic wake. Scholars theorize that the regulus is a close relative of the larger guivre, and represents poison as its mighty cousin symbolizes disease.

Reguli hate the company of their own kind; they are too selfish to ever cooperate and consider each other rivals to be eliminated. This racial madness is in part responsible for the rarity of reguli, which reproduce only asexually and very infrequently. It is also the root cause of their hatred of mirrors, for a regulus’ killer instinct works too quickly and it can easily target itself with its deadly gaze if it sees its own reflection. The only creatures a regulus has any care for are mundane snakes, which it can speak to and control effortlessly. It is not for nothing that the regulus is called “King of Serpents” and a regulus’ favored demesne is usually filled to the brim with venomous and constrictor snakes of all sizes and kinds.

In combat, reguli weave throughout the battlefield, exposing all enemies to their venomous aura and killing the survivors with their gaze. If forced into melee, they respond with their bites, which are relatively weak but carry a debilitating poison. Reguli do not hesitate to flee if a battle turns against them, and reguli lairs always have at least one escape route.

Regulus CR 11
XP 12,800
LE Medium dragon
Init +11; Senses blindsense 60 ft., darkvision 60 ft., low-light vision, Perception +17, scent
Aura deadly venom (30 ft., Fort DC 20)
Defense
AC 23, touch 17, flat-footed 16(+7 Dex, +6 natural)
hp 126 (12d12+48)
Fort +12, Ref +15, Will +12
DR 10/magic and silver; Immune paralysis,poison, sleep effects; SR 21
Vulnerability mirrors
Offense
Speed 30 ft., climb 30 ft., swim 30 ft.
Melee bite +19 (1d6+3 plus poison)
Special Attacks death gaze
Spell-like Abilities CL 12^th, concentration +17
Constant—speak with animals (snakes only)
At will—charm monster (DC 19, snakes or snake-like creatures only)
Statistics
Str 14, Dex 23, Con 19, Int 17, Wis14, Cha 20
Base Atk +12; CMB +14; CMD 31 (cannot be tripped)
Feats Combat Expertise, Dodge,Improved Initiative, Iron Will, Vital Strike, Weapon Finesse
Skills Acrobatics +19, Bluff +20, Climb +25, Diplomacy +20, Intimidate +20, Perception +17, Sense Motive +17, Stealth +22, Swim +25
Languages Aklo, Common, Draconic, Infernal
Ecology
Environment warm and temperate land
Organization solitary or court (1 plus 5-25 HD of charmed snakes)
Treasure triple standard
Special Abilities
Aura of Deadly Venom (Su) A regulus is constantly surrounded by a 30 foot radius of poisonous vapors that function as the cloudkill spell, except that they do not provide concealment. All creatures in the aura with 3 or fewer Hit Dice die with no save. Creatures with 4-6 Hit Dice must succeed a DC 20 Fortitude save or die; success means the creature takes 1d4 points of Constitution damage. Creatures with 7 or more Hit Dice must succeed a DC 20 Fortitude save or take 1d4 points of Constitution damage; on a passed save, the damage is halved. Creatures in the aura of deadly venom must make this save every round. A strong or stronger wind can disperse the aura of deadly venom, but the regulus can recreate it as a free action once the wind has calmed. This is a poison effect. All snakes are immune to this effect. The save DC is Constitution based.
Death Gaze (Su) Once per round as a standard action, a regulus can focus its gaze on a living creature within 60 feet. Any creature so affected must succeed a DC 21 Fortitude save or take 12d6+12 points of negative energy damage. A successful save reduces the damage to 3d6+12. This is a death effect, and methods used to avoid gaze attacks can protect against a regulus’ death gaze. The save DC is Charisma-based.
Mirror Vulnerability (Ex) Whenever a regulus sees itself in a mirror, it must succeed a DC 25 Will save in order to recognize the reflection as itself. If the regulus fails to recognize the reflection, it will attack its reflection, and therefore itself, with its death gaze on its next turn. Once a regulus has attacked its own reflection once, it recognizes the nature of the image and will not attack its own reflection for the next 24 hours.
Poison (Ex) Bite—injury; save Fort DC 20; frequency 1/round for 4 rounds; damage 1d2 Con drain; cure 2 consecutive saves. The save DC is Constitution based.