Amphisbaena (5e Creature)
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Large monstrosity, unaligned
Regeneration. The amphisbaena regains 10 hit points at the start of its turn. If the amphisbaena takes acid or fire damage, this trait doesn't function at the start of the amphisbaena's next turn. The amphisbaena dies only if it starts its turn with 0 hit points and doesn't regenerate.
Multiattack. The amphisbaena makes two bite attacks.
Bite. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 7 (1d6 + 4) piercing damage, and the target must make a DC 13 Constitution saving throw, taking 10 (3d6) poison damage on a failed save, or half as much damage on a successful one.
Amphisbaena are vicious two-headed serpents noted for their ability to regenerate. The poison of an amphisbaena is about as potent as that of an ordinary serpent, though the fact that it is administered twice by the creature's twin mouths contributes greatly to its lethality.