This seven-headed serpent has serrated fangs, and moves with incredible speed despite its massive bulk.
Mythic Hydra CR 9/MR 3
N Huge magical beast (mythic)
AC 20, touch 9, flat-footed 19 (+1 Dex, +11 natural, –2 size)
hp 117 (7d10+79); fast healing 7
Fort +10, Ref +8, Will +4
Speed 40 ft., swim 40 ft.
Melee 7 bites +8 (1d8+3 plus bleed)
Space 15 ft.; Reach 15 ft.
Str 17, Dex 12, Con 20, Int 2, Wis 11, Cha 9
Base Atk +7; CMB +12; CMD 23 (can't be tripped)
SQ hydra traits, regenerate head
Environment temperate marshes
Fast Healing (Ex) A mythic hydra's fast healing ability is equal to its current number of heads (minimum fast healing 5). This fast healing applies only to damage dealt to the hydra's body.
Hydra Traits (Ex) A mythic hydra can be killed by severing all of its heads or slaying its body. Any attack that is not an attempt to sever a head affects the body, including area attacks or attacks that cause piercing or bludgeoning damage. To sever a head, an opponent must make a sunder attempt with a slashing weapon targeting a head. A head is considered a separate weapon with hardness 0 and hit points equal to the hydra's Hit Dice. To sever a head, an opponent must deal enough damage to reduce the head's hit points to 0 or fewer. Severing a head deals damage to the hydra's body equal to the hydra's current Hit Dice. A hydra can't attack with a severed head, but takes no other penalties.
Regenerate Head (Ex) When a mythic hydra's head is destroyed, two heads regrow in 1d4 rounds. A mythic hydra can't have more than twice its original number of heads at any one time. To prevent new heads from growing, at least 5 points of acid or fire damage must be dealt to the stump (a touch attack to hit) before they appear. Acid or fire damage from area attacks can affect stumps and the body simultaneously. A hydra doesn't die from losing heads until all its heads are cut off and the stumps are seared by acid or fire.
A mythic hydra is a deadly combination of bites, lunges, speed, and durability. Descended from the very first of its kind, it may run wild. Or created whole by some divine agent, it could be placed as a guardian of a sacred site or a portal to the underworld. Some mythic hydras are reputed to have poisonous breath and blood, or to be so toxic that they corrupt the ground they crawl upon.