Amphisbaena (CR 5)
Large Magical Beast
Alignment: Always Neutral
Initiative: +3 (Dex); Senses: darkvision 60 ft., low-light vision, scent, Listen +13, and Spot +13
AC: 17 (-1 size, +3 Dex, +5 natural), touch 12, flat-footed 14
Hit Dice: 6d10+12 (45 hp)
Fort +7, Ref +8, Will +3
Speed: 40 ft., climb 20 ft.
Space: 5 ft. (coiled)/10 ft.
Base Attack +6; Grapple +11
Attack: Bite +8 melee
Full Attack: 2 bites +8 melee
Damage: Bite 1d6+1 plus poison
Special Attacks/Actions: Poison
Abilities: Str 13, Dex 16, Con 15, Int 2, Wis 12, Cha 3
Special Qualities: hardened corpse, immunity to cold
Feats: Alertness; Combat Reflexes; Weapon Finesse
Skills: Balance +15, Climb +11, Hide +6, Listen +13, Spot +13, and Tumble +9
Advancement: 7-9 HD (Large); 10-18 HD (Huge)
Climate/Terrain: Temperate marshes
Poison (Ex): Bite, Fortitude DC 15, initial and secondary damage 1d8 Constitution. The save DC is Constitution-based.
Hardened Corpse (Su): Just before death, an amphisbaena attempts to bite one head with the other. If it succeeds, its body turns to hardened stone upon death.
Skills: An amphisbaena has a +4 racial bonus on Hide and Tumble checks, a +8 racial bonus on Climb, Listen, and Spot checks, and a +12 racial bonus on Balance checks.
An amphisbaena can always choose to take 10 on a Climb check, even if rushed or threatened. An amphisbaena can use either its Strength or its Dexterity modifier for Climb checks, whichever is better.
Feats: An amphisbaena's Combat Reflexes feat allows it to use both of its heads for attacks of opportunity each round.
An amphisbaena can attack with both its heads simultaneously, and each head may strike a separate target if desired. Moreover, an amphisbaena's two heads give it an advantage over normal snakes in that it can feed and defend against threats at the same time.