A huge fearsome serpent with a head at each end of its 10- to 15-foot body

The Amphisbaena, also called a giant two-headed snake, is a huge fearsome serpent with a head at each end of its 10- to 15-foot body; each head can attack a different opponent within that range, and any opponent bitten must save vs. Poison or die. An amphisbaena can clasp its mouths together, forming a hoop, and in this form move at double speed over relatively smooth terrain (especially including roads or trails) for an extended period of time. Obviously it cannot attack while moving in this fashion.

Two-headed snake that rolls like a hoop, immune to cold

All giant snakes are carnivorous and can be found in every type of climate except for the coldest. Amphisbaena are 6-ft long snakes with a head at both ends of its body. Both heads are capable of delivering a poisonous bite and victims must save vs poison or die instantly. Its method of travel is as bizarre as the creature's appearance, one head of this unusual snake will grab the neck of the other and the creature then rolls like a hoop upon the ground! Amphisbaena are carnivorous and like most other reptiles, are cold-blooded and prefer warmer climes. Oddly enough, the amphisbaena is immune to cold based attacks, though the sages are at a loss as to why this is so.