Asmodeus Poisonteeth (also known as Giant Ice Eyes by the shrews) was the last in a long line of giant adder snakes whose family resided in a sealed network of tunnels in the Quarry. Asmodeus was incredibly dangerous, often going out on silent hunts in Mossflower Woods, and often surprised creatures who were hiding in the same hiding place as he. Asmodeus was also a collector of trophies or treasures from his fallen victims; foxes' tails and woodpigeon feathers, but his crowning trophy was when he was able to steal the sword of Martin the Warrior from King Bull Sparra, killing Greytail in the process, while the two were hunting in the woods. Proud of his prize, Asmodeus took it back to his lair and treasured it closely.
Many seasons later, during Cluny the Scourge's war on Redwall Abbey, Matthias, on a quest to find the sword to save his home, tracked its location to Asmodeus's lair, and, enlisting Log-a-Log and the Guosim to help in his quest, was successfully able to sneak into the quarry and steal the sword while Asmodeus slept. Asmodeus was awoken before they could escape, however, and pursued them through the tunnels to retrieve "his" sword. Asmodeus then cornered them in a cul-de-sac, and hypnotized both of them to stand down their weapons, and was poised to kill them, but then Matthias had a vision of Martin the Warrior, who was able to break him out of his trance, and Matthias struck.
Log-a-Log snapped out of the trance a few minutes later, and found that Matthias had beheaded Asmodeus, who would never again terrorize Mossflower.